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Glossary of Terms

Glossary of Terms

18-8 ss A grade of stainless steel including 18% chromium and 8% nickel; typically used on bolts, screws and nuts.

300 Series ss Generic reference to any stainless steel grade in the numerical 300 series family.

304 ss Vacuum grade stainless steel; can be easily machined and welded; very low outgassing properties.

304L ss Very low-carbon stainless steel.

316 ss Vacuum grade stainless steel; low magnetic permeability.

A or Amp Ampere; unit of electric current.

Absorption In optics, a source of loss or attenuation that is due to material properties of an optical fiber.  Absorption is quite often wavelength dependent.

Acceptance Angle The maximum cone half-angle for which incident light is captured by and will travel through the optical fiber.

AC Alternating current.

Accuracy The maximum expected difference between the actual and a desired position for a given input. Highly dependent on method of actual position measurement.

Accuracy, Absolute The output of a system versus the commanded or ideal input.

Actuator A portion of a device that provides motion to the internal parts of the device; typically manual or electro-pneumatic.

Adapter Provides a transition from one method of sealing to a different method of sealing, such as metal seal to elastomer seal.

aka The abbreviation for "also known as".

AL or Al Aluminum.

Alumel ® The trade name for a nickel alloy that is used with Chromel ® in thermocouples; a registered trademark of Hoskins Manufacturing Company.

Aluminum 6061-T6 Vacuum grade aluminum.

AM-350 A precipitation hardened stainless steel used in welded bellows; similar to 304L with a longer life in cycling.

Amp or amps Ampere; unit of electric current.

ANSI American National Standards Institute.

ASA American Standards Association, replaced by ANSI.

ASME American Society of Mechanical Engineers.

ASTM American Society for Testing and Materials.

Atm or atmos Atmosphere; used in pressure measurement reference.

Attenuation in optics; The amount of light loss experienced in an optical fiber or optical media as a function of length.  For optical fiber it is usually expressed in db (decibels) per kilometer (km).

AWG American Wire Gage; corresponds with the number of operations of drawing a wire, thus a larger number, which represents more operations, results in a smaller diameter wire; aka Brown & Sharpe gauge; there are many wire gauge methods.

BA Bayard-Alpert (gauge); method of vacuum measurement.

Backlash The maximum magnitude of an input that produces no measurable output upon reversing direction. Typically the result of poor meshing between drivetrain components as in lead screw threads.

Bandwidth The range of frequencies (or wavelength) which are useful for a device or system.  In optical fiber, it is a measure of information carrying capacity.  The frequency bandwidth is usually described as the frequency where the optical power is one-half the power at zero frequency.  The wavelength bandwidth is usually expressed in terms of wavelength-dependent attenuation or transmission, and is not necessarily related to the signal bandwidth.

Bar A unit of pressure measurement; in vacuum applications, used as millibar.

BC Bolt circle; the center to center distance of two bolt holes on the same diameter; generally may be used in specifying any centerline to centerline distance of elements on the same diameter; sometimes used in place of the connector circle (CC) for pins on an electrical connector.

Bending Loss Loss in an optical fiber caused by bending of the fiber.  This loss is usually due to internal light paths exceeding the critical angle for TIR.  Both micro-bending and macro-bending are characteristics of optical fibers.

Bend Radius The radius of a drum or mandrel around which an optical fiber or cable is wrapped or wound. 

Best Way A method of shipment to be selected by Accu-Glass Products, Inc. which would be appropriate for the type of product to be shipped.

Blind hole A drilled hole that does not break through the metal; maintains the vacuum integrity of the drilled piece.

Blind tapped A tapped blind hole; female threads inside a hole that does not break through the metal; maintains the vacuum integrity of the drilled and tapped piece.

BNC Bayonet Naval Connector; a specific type of electrical connector that attaches without threads; used in 50 ohm and 75 ohm coaxial low power instrumentation transmission lines.

Bolt length The portion of a bolt excluding the head; may be threaded completely or have a shank with partial threading.

Bonnet The flanged connection of two parts of a valve; the flanges between the actuator and body of a valve.

Buffer The buffer is an outer coating on an optical fiber.

Buna-N® A DuPont Dow Elastomers registered trademark brand name of a type of elastomer seal; butyl material which has excellent resistance to gas permeation; an early vacuum seal, generally displaced by Viton®.

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Cable, Fiber Optic A package or assembly for an optical fiber or fibers that may include buffering, strength members and/or an outer jacket.

Capture groove A counter bore in a flange that a gasket seats into; keeps a gasket from moving outside its range of correct positioning.

Carriage The movable parts in a gate valve, including wheels, pins, springs, supports, etc.; the back side of the flat O-ring sealed gate in a gate valve.

cc Cubic centimeter; metric unit of volume measurement.

CC Connector circle; the center to center distance of two pins on the same diameter of an electrical connector.

CCW Counterclockwise.

CE Compliance European safety standard; similar to UL listing in the USA.

CF flange, CF metal seal flange; The abbreviation for a Conflat ®-compatible metal sealed vacuum flange.

Chromel® An alloy that is predominantly nickel with chromium that is used with Alumel ® in thermocouples; a registered trademark of Hoskins Manufacturing Company.

CIF Carriage and Insurance paid to customer's delivery address.

Cladding A low refractive index optical material that surrounds the core of an optical fiber.  It is used to cause reflection of the core light while preventing surface contact from scattering or the generation of frustrated internal reflection.  In all-glass fibers, the cladding is glass.

Clearance holes Holes that are drilled completely through a metal piece without threads; also called through holes or thru holes.

Conflat ® A registered trademark of Varian Corporation, the original metal sealed flange.

Core The light-conducting portion of an optical fiber having a higher refractive index than the cladding.  Usually made of a pure synthetic silica, but can be a doped material to provide special fiber characteristics.

Counter bore A straight bore partially through a metal piece; sometimes concentric with a smaller bore.

CSA Canadian Standards Association; comparable to United Laboratories approval in the USA.

CSR Customer Service Representative.

CVD Chemical vapor deposition; a method of depositing material on a substrate using a chemical reaction.

CW Clockwise.

DAP or Diallyl Phthalate; a high vacuum compatible material used in connectors.

DC Direct current.

Decibel The standard unit used to express gain or loss and relative power levels.  The decibel (dB) = -10 log(PoPi), where P0 is the power-out and Pi is the power-in.

Delrin ® An insulating plastic that is machinable and non-marring; a registered trademark of E.I. du Pont de Nemours and Company.

DWDM Dense wavelength-division multiplexing; see WDM.

DIA or dia Diameter.

Dicronite A dry film lubricant used on linear and ball bearings; modified tungsten disulfide in lamellar form; inert, corrosion resistant, non-magnetic and UHV compatible throughout a wide temperature range.

DIN Deutsche Industrie Norm (German); German industry standard.

Display Resolution The smallest motion detectable by a motion device's precision rule, micrometer or motor controls.

DN Diamétre Nominal (French); nominal diameter, usually referring to vacuum tubing internal diameter.

Doped (synthetic) fused silica  See Fused Silica

ea The abbreviation for each.

EB, E-B, e-beam or other variations Electron beam.

Eccentricity Sometimes called concentricity, eccentricity in a rotary device is the deviation of the center of rotation from its mean position as the device turns.

Effective numerical aperture See Numerical aperture (NA).

Elastic limit The point beyond which permanent deformation of a material occurs; aka yield point.

Elastomer A flexible material for completing a vacuum seal between two flat surfaces, usually ISO flanges; colloquially "rubber".

Electro-pneumatic Method of actuating a device using a compressed gas which is controlled by an electrical solenoid valve.

Electropolishing Removes a small amount of surface metal from any shape of stainless steel; provides an attractive high-luster finish plus deburring.

EMF Electromagnetic Frequency.

Error The difference between an obtained performance parameter and the ideal or desired result. Errors fall into two primary categories, on-axis and off-axis errors.

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FEP Fluorinated ethylene-propylene.

Fiber optics A branch of optics that deals with the transmission of light through fibers, tubes or thin rods of a transparent material.

Fixed flange Non-rotatable; composed of a single machined piece; when welded to tubing or a chamber, the bolt holes cannot be rotated to align with bolt holes of another flange.

Flush mount One flange is welded directly to the back of either another larger flange or a flat surface; typically the total thickness is the sum of the two individual thicknesses.

FOB Freight on board; the point at which transfer of ownership of a product occurs.

FPT Commonly used abbreviation for female pipe thread.

Friction Friction is defined as the resistance to motion between surfaces in contact. Friction can be constant or it can vary with speed. Elements contributing to overall friction may be in the form of drag, sliding friction, system wear or lubricant viscosity.

Friction, Static The friction that must be overcome to impart motion to a body at rest. Since static friction is higher than sliding friction, the force which must be applied to impart motion is greater than the force required to keep the body in motion. As a result, when a force is initially applied, the body will begin to move with a jump in some unpredictable and unrepeatable manner, producing non-linear, non-repeatable motion.

FT or ft Foot; unit of length measurement.

F/T or f/t Abbreviation for feedthrough.

Fused quartz See Fused silica.

Fused silica  A silicon dioxide (SiO2) in its amorphous (glassy) state.  Silica is silicon dioxide (SiO2). Synthetic fused silica is amorphous silicon dioxide that has been produced through chemical deposition rather than refinement of natural ore.  Doped (synthetic) fused silica is amorphous silicon dioxide that has been produced through chemical deposition.  It has been intentionally doped with trace elements to adjust the optical properties of the glass.  Quartz is a natural grade of crystalline silicon dioxide (SiO2).  Fused quartz is a natural grade of amorphous SiO2.  Typically produced from the melting (fusing) of crystalline quartz and refined such that an amorphous (glass) is formed.

Gasket Any material between two sealing surfaces; either metal or elastomer material; typically rectangular in cross-section but may also be circular in cross-section.

Gate The flat plate in a gate valve that makes a seal between the two sides of a valve; includes a groove to hold an elastomer O-ring which completes the seal.

Gear Ratio, Drive Train A motion instrument's drive train gear ratio is the relationship between received input motion and the delivered output motion. Ratios are expressed in the numerical notation a:b, where "a" represents the received motion or device input in revolutions or some other unit, and "b" represents the delivered or resulting output motion in revolutions for rotary devices or 1 inch of travel in linear motion instruments.

gpm Gallons per minute; unit of liquid volume flow.

gps Gallons per second; unit of liquid volume flow.

Graded seal The portion of a glass component that changes from one material to another; typically the transition from Pyrex® to quartz tubing.

High-OH Fiber High oxygen hydrogen content.

HV High vacuum; typically between 10-3 to 10-8 Torr.

Hybrid A combination of two different methods of sealing, such as metal seal to elastomer seal; an adapter.

Hysteresis The difference in the absolute position of an object for a given commanded input when approached from opposite directions. It is due to elastic forces accumulated in various drivetrain components, leadscrew wind-up, for instance. Often confused with backlash.

Hz Hertz; frequency measured in cycles per second.

ID or I.D. Internal diameter or inner dimension; usually of tubing or a hollow bore through a metal piece.

IEEE Institute of Electrical and Electronics Engineers.

IGT Ionization gauge tube; used with a gauge to measure pressure.

Index of refraction (n) The ratio of the velocity of light in a vacuum to the velocity of light in a refractive material at a given wavelength.

in. Inch; without period combined units.

in-oz inch-ounce; a US system measure of torque.

Insert Part of a rotatable flange; the smaller part of a rotatable flange that is welded to a tube; includes the sealing knife-edge; requires a receiver to complete a vacuum seal.

IR Infrared light.

ISO International Standards Organization.

J or joule The SI unit of work; newton-meter.

Jack The name of a female connector, consisting of one or more sockets.

Jacketing Usually the outer material used on an optical fiber or fiber bundle.

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Kalrez® 4079 A perfluoroelastomer useful in corrosive or high temperature applications.

Kapton® A polyimide material in film; a compact, lightweight, and mechanically tough insulation material; it has very low outgassing properties, making it ideal for use in UHV applications; a registered trademark of E.I. du Pont de Nemours and Company.

KF flange The smaller ISO flanges; originally Klein Flange developed in Germany, "klein" meaning small; smaller components of a complete ISO flange family.

kg/mm Kilograms per millimeter.

Knife-edge The sealing detail on a metal seal flange; the portion of a metal seal flange that bites into a gasket between two identical size flanges.

Kovar® - Alloy 29-17 The Carpenter Technology registered trademark brand name of a highly magnetic nickel-iron alloy; provides a transition between stainless steel and glass materials in viewports or other components; has a phase shift at -80°C and therefore not suitable for cryogenic applications.

Krytox ® A vacuum compatible lubricant; a registered trademark of DuPont Company.

kV Kilovolts; measurement of electrical voltage.

kVDC Kilovolt Direct Current, a measure of voltage.

kV/mm Kilovolt per millimeter.

kW Kilowatts; measurement of electrical power.

LB or lb. Pound; unit of weight measurement.

LB ƒ or lb ƒ Pound; unit of force measurement; frequently the " ƒ" is omitted when the context is clear.

lb-ft Pound-foot; unit of torque measurement; sometimes written lb ƒ-ft.

lb-in2 A measure of inertia.

LCD Liquid crystal display; typically used on instrumentation.

Leak check grooves Narrow radial grooves machined into a metal seal flange between the outer surface and the capture groove for a gasket; typically not on flanges larger than 10-inch OD.

LF flange The larger ISO flanges; name for the larger components of a complete ISO flange family.

Live length The portion of a bellows that can provide motion; the convoluted portion of a formed bellows.

LN 2 or LN Liquid nitrogen.

Load Capacity, Stage The maximum centered load that can be placed directly on an XYZ motion stage and is typically limited by the load capacity of the bearings

Load Capacity, Lateral or Moment Also called side or bending load capacity, it is the maximum load that can be applied perpendicular to a shaft's axis of motion.

Load Capacity, AxialThe maximum centered and balanced compressive or tensile load that can be applied to a stage's or shaft's longitudinal or parallel axis of motion.

Load-Lock A method of introducing product into a vacuum chamber via an intermediate chamber; allows sample manipulation without significantly affecting the vacuum of the main chamber.

LV Low vacuum; typically between atmosphere and 10-3 Torr.

Matte finish A bead blast finish on standard tubing.

MAX or max Maximum.

MESA Modular Equipment Standards Architecture; replaced by MESC.

MESC Modular Equipment Standards Committee.

MHV Miniature high voltage; used in medium power applications; similar to BNC series, but do not mate with BNC.

micron ( µm) A unit of length equal to .000001 meter.

mil A unit of length equal to .001 inch.

min A Minimum or minute, depending on context.

Minimum Incremental Motion The smallest motion a device is capable of delivering reliably, not the smallest display resolution increment.

MPI Mechanical position indicator; available on most electropneumatic valves; utilizes mechanical microswitches to provide open/closed circuits which may be used for position indication, interlock circuitry, etc.; requires customer wiring.

MPT Commonly used abbreviation for male pipe thread.

Multimode fiber An optical waveguide that will allow more than one mode to propagate (EIA).

Mu-metal A composite of rare earth metals used to provide a magnetic shield around sensitive instrumentation.

Mylar ® A strong polyester film that has superior strength, heat resistance, and excellent insulating properties; a registered trademark of E.I. du Pont de Nemours and Company.

mV millivolt.

NEMA National Electrical Manufacturers Association.

Ni-Fe Nickel-iron alloy.

NIR Near infrared light.

NIST National Institute of Standards and Technology.

Nanometer (nm) A unit of measure most often used for light in the visible (1x10-9 meters).  The peak of the human eye sensitivity is at a wavelength of 550 nm (green light).  In the UV range where Angstroms are still sometimes used, 200 nm is 2000 A.  In the near infrared where microns ( µm) are used, 1000 nm is 1 micron ( µm)

No. The abbreviation for number.

Nominal The approximate or rounded-off dimension used to designate the size of an object, such as a flange or tube; abbreviated "Nom." or "nom.".

Non-rotatable A flange machined from a single piece of material; once welded to tubing or a chamber, the bolt holes are no longer rotatable for alignment purposes.

Non-terminated Bare wires or cables without any connector attached.

NPT National Pipe Taper; a specific taper to a threaded hole which provides a pressure seal between male and female threads; sometimes referred to as National Pipe Thread.

Numerical aperture (NA) In optical fiber, the sine of the maximum acceptance half-angle, θmax, times the refractive index of the core (assuming an air-to-core interface).  The larger the NA, the greater the amount of light that is accepted into the fiber for propagation to the distal end.  NA=n1 * sin( θmax) , where n1 = 1 for air.

NW Nenn Weite (German); nominal diameter, usually referring to vacuum tubing internal diameter.

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OD Outside diameter or outer dimension; usually of tubing or any circular or spherical piece, but can also apply to any shape.

OEM Original equipment manufacturer.

OFE copper Oxygen free electronic grade copper; also called oxygen free electrolytic or simply oxygen free; replaces OFHC.

Optics A branch of physical science dealing with the propagation and behavior of light.  In a general sense, light is that part of the electromagnetic spectrum that extends from X-rays to microwaves and includes that radiant energy that produces the sensation of vision.

OFHC copper Oxygen free, high conductivity; a trade name for vacuum compatible copper that is no longer being manufactured; replaced by OFE copper.

O-ring An elastomer vacuum seal available in various materials; torus or doughnut shaped, typically circular in cross-section; may be a dynamic or static seal.

oz Ounce; unit of weight measurement.

oz ƒ Ounce; unit of force measurement; frequently the " ƒ" is omitted when the context is clear.

oz-in 2 A measure of inertia.

oz-in Ounce-inch; unit of torque measurement.

PEEK (polyetheretherketone); a crystalline material with excellent mechanical and electrical insulation properties; it has very low outgassing properties, making it ideal for use in UHV applications.

pf Picofarad; unit of electrical capacitance measurement.

pf/m Picofarads per meter, a measure of capacitance.

PI Position indicator; available on most valves; utilizes stationary magnetic Reed switches and a movable magnet.

PIN The name of a single male contact.

Pitch The spacing of threads on a shaft; related to threads per inch.

pkg the abbreviation for package.

Play Uncontrolled movement due to looseness of mechanical parts. Usually increases with the components age. Play is a contributor to backlash.

plt The abbreviation for plated, as in Ni-plt Zn (Nickel-plated Zinc).

Plug The name of a male connector, consisting of one or more pins.

p/n or pn The abbreviation for part number.

Polyimide is an aromatic, linear polymer typically produced by condensation reaction, such as polymerizing aromatic dianhydride and aromatic diamine.  It is not a true thermoplastic because it thermally degrades before its glass transition temperature.  It is not a true thermoset because it is not cross linked.  The most notable properties are its solvent resistance, barrier properties, and performance at both high and low temperatures.

Poppet The movable portion of an angle valve; includes a groove to hold an elastomer O-ring which completes the seal.

Position Stability The ability to maintain a constant position over time. Variation from stable position is called drift. Contributors to drift include worn parts, migration of lubricant, and thermal variation.

Precision Also known as repeatability, it is the range of deviations in output position that will occur for 95% of the motion excursions from the same error-free input. Accuracy and precision are not the same.

PSI Pounds per square inch; unit of pressure measurement.

PSIA Pounds per square inch absolute; pressure measured with respect to zero pressure.

PSIG Pounds per square inch gauge; pressure measured with respect to that of the atmosphere.

PTFE Polytetrafluorethylene; self-lubricating, non-compressible, inert and low outgassing material for dynamic seals.

PVC Polyvinyl chloride; typically used in low vacuum applications such as roughing lines.

PVD Physical vapor deposition; a method of depositing material on a substrate using evaporation.

QMS Quadrupole mass spectrometer.

Quad-Ring An elastomer used in dynamic seals; typically "U" shaped in cross-section.

Quartz A very hard mineral composed of silica, SiO2, found worldwide in many different types of rocks, including sandstone and granite.

Rads A measure of radiation.

Receiver Part of a rotatable flange; the larger outer part of a rotatable flange that includes bolt holes; may be rotated to align bolt holes prior to completing a vacuum seal.

Reducer A fitting that changes diameter from one size to another within a single method of sealing, such as metal seal to metal seal; contrasted with Adapter.

Repeatability The ability of a motion instrument to reliably achieve a commanded position over many attempts regardless of the direction from which the position is approached.

RF Radio frequency.

RGA Residual gas analyzer.

RH Relative Humidity.

RMS Root-mean-square; a calculation to determine an average of fluctuating values; electrical or surface finish measurement.

Roll-up A cylindrical shaped section of stainless steel that is welded internally for vacuum integrity and stitch welded externally for strength; for vacuum chambers or "tubing" greater than 10 inches in outer diameter.

Rotatable flange Composed of two machined pieces: an insert and a receiver; used for bolt hole alignment only; the insert is welded to tubing and the receiver slides over the insert; the receiver bolt holes can be rotated to align with bolt holes of another flange, once bolts are inserted the receiver cannot be rotated.

RPM or rpm Revolutions per minute; measurement of rotational speed.

Runout The linear, not angular, portion of off-axis error. It is the deviation between ideal straight line motion and actual measured motion in a translation stage. Runout has two orthogonal components, straightness, a measure of in-plane deviation, and flatness, the out-of-plane deviation.

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SAE Society of Automotive Engineers.

SEMI Semiconductor Equipment and Materials International.

Sensitivity The minimum input required to produce output motion or the ratio between output motion and input drive; applicable particularly to manually actuated motion devices.

Setback The distance from the sealing face of a flange to the tubing counterbore.

SHV Safe high voltage; similar to MHV series, except SHV cable connector center contacts do not protrude from connector ends which makes them safer in a disconnected condition.

SI Système International d'Unités (French); unified system of measurement including the metric system, electrical units such as Amperes, Volts, etc.

SMA A high frequency coaxial feedthrough designed per Mil Spec Mil-C-39012/58F.

Snells law The relationship between an incident ray at angle I in refractive index media n1, and the refracted (or reflected ray) at angle R in refractive index media n2 is: n1 * Sin( I) = n2 * Sin( R)

Socket The name for a female contact, either accepting a single pin or a plug.

Spectrum, Visible The region of the electromagnetic spectrum to which the retina is sensitive and by which the eye sees.  It covers the range from about 400 to 750nm in wavelength.

Spring rate The amount of force required to compress a guided bellows one linear inch; given in pounds per inch (lbs/in).

Squirm Arbitrary lateral movement of a bellows.

SS, SST, ss or sst Abbreviation for Stainless Steel, any grade.

Stainless steel In general, an iron-chromium alloy; corrosion resistance is enhanced by the addition of nickel.

Static bend radius The minimum radius a bellows can be curved without encountering permanent deformation.

Std Atm cc/sec He Leak rate measurement.

Swagelok® The Swagelok Company registered trademark brand name tube fitting providing UHV compatible connections on fractional inch tube sizes; uses a compressible ferrule; requires clean tube end only.

Tangents Lengths of straight tubing added to elbows so that centerlines of straight sections are tangent to curved centerline.

Tapped holes Drilled holes that have female threads cut into them; also called threaded holes.

TC Thermocouple; method of measuring heat and therefore indirectly measuring vacuum pressure.

Temp or temp Abbreviation for temperature.

Threaded holes Drilled holes that have female threads cut into them; also called tapped holes.

Through or Thru holes Drilled holes that are smooth and completely through the material; also called clearance holes.

TIG Tungsten inert gas; a method of welding which keeps the weld shielded from corrosive atmosphere by bathing the area with an inert gas during the process.

Tilt The angular portion of off-axis error. It is the deviation between ideal straight line motion and actual measured motion in a translation stage. Tilt and wobble have three orthogonal components commonly referred to as roll, pitch, and yaw.

Torr A unit of pressure measurement; one atmosphere equals 760 Torr; sometimes written torr.

TSE Technical Sales Engineer.

Typ or typ Typical; applies to all occurrences of a feature in a drawing.

Type-D Subminiature feedthrough Based on MIL-C-24308 specifications for pin arrangements; identified by a "D" or keystone shape.

Type N feedthrough Low instrumentation voltage feedthrough for matched 50 ohm impedance rating applications.

UHV Ultrahigh vacuum; defined by the American Vacuum Society as the pressure range between 7.5 x 10-10 to 7.5 x 10-13 Torr; British and German standards define UHV as 10-8 Torr or better.

UL Underwriter's Laboratories; typically a stamp of approval for acceptable electrical safety standards in the USA.

Ultra-Low-OH Ultra-low oxygen hydrogen content.

UNC Unified National Coarse; referring to bolt threads.

UNF Unified National Fine; referring to bolt threads.

UNS Unified Numbering System.

UPS United Parcel Service.

UTA Common abbreviation for up-to-air.

Ultraviolet (UV) A wavelength range below the lower end of the visible spectrum.  The UV most often refers to the range from 400nm down to 200nm.

V Volt; unit of electrical voltage.

VAC Alternating current voltage.

VCR® The Swagelok Company registered trademark brand name tube fitting providing UHV compatible connections on fractional inch tube sizes; uses a replaceable metal gasket; requires mating connector installed on tubing.

VDC Direct current voltage.

Vespel® The DuPont Dow Elastomer registered trademark brand name of a high vacuum compatible polyimide material used for bearings; may be used without lubrication.

VIS Visible light.

Viton® The DuPont Dow Elastomers registered trademark brand name of a fluorocarbon elastomer; first introduced in the 1950s; wide use in vacuum applications.

V/mm Volt per millimeter.

Wavelength In fiber optics, the length of one wave cycle of a light wave.

WDM Wavelength-division multiplexing; a technology providing increased transmission capacity of fiber optics; sometimes called DWDM.

Wobble The angular deviation of the axis of rotation over one complete revolution.

WT or wt Weight.

W x H x D Rectangular dimensions; Width x Height x Depth.

XHV Extreme high vacuum; defined by the American Vacuum Society as below 7.5 x 10-13 Torr.

Yield point The point beyond which permanent deformation of a material occurs; aka elastic limit.

Zero-length Any flanged device that has a total overall thickness equal to the thickness of the flange itself.

& ampersand; the symbol for "and".

Å Angstrom; unit of length; 1 Å = 10-10 m.

@ the symbol for "at".

°C degrees Centigrade or Celsius; unit of temperature

°F degrees Fahrenheit; unit of temperature.

µ Mu; unit of magnetic permeability; also the symbol for micron as µin, micro-inch.

# the symbol for "number" or "pound" weight, depending on context.

Omega; ohm, unit of electrical resistance or impedance .

/km Ohms per kilometer, a measure of electrical resistance.

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