Air Gages Information

Air gageAir gages use pneumatic pressure and flow to measure and sort dimensional attributes. They provide a high degree of speed and accuracy in high-volume production environments. Air metrology instruments can provide comparative or quantitative measurements such as:

  • thickness
  • depth
  • internal diameter (ID)
  • outer diameter (OD)
  • bore
  • taper
  • roundness

Air gages and gaging systems may also use an indicator or amplifiers such as air columns combined with air probes or gages.


There are several types of air gages. Air plugs are production-quality, functional gages for evaluating hole and slot dimensions or locations against specified tolerances. Air rings are also production-quality, functional gages, but are used for evaluating specified tolerances of the dimensions or attributes of pins, shafts, or threaded studs. Air gaging systems or stations are large, complex units available in bench-top or floor-mounted configurations. These systems often include several custom gages for OEM applications, as well as fixtures or other components for holding or manipulating parts during inspection. Air probes, or gage heads, are also used in conjunction with other gages, and connect to remote displays, readouts, or analog amplifiers.


Test indicators and comparators are instruments for comparative measurements where the linear movement of a precision spindle is amplified and displayed on a dial or digital display. Dial displays use a pointer or needle mounted in a graduated disc dial with a reference point of zero. Digital displays present metrology data numerically or alphanumerically, and are often used with air gages that have data output capabilities. Remote gages are used on electronic or optical gages, probes, or gage heads that lack an integral gage. Air gages can use the English measurement system (e.g., inches) or the metric system (e.g., centimeters).


Air gages use changes in pressure or flow rates to measure dimensions and determine attributes. Back pressure systems use master restrictor jets, as well as additional adjustable bleeds or restrictions, to measure pressure changes and adjust for changes in air tooling. Flow systems use tubes or meters to measure flow rates through air jets, orifices, or nozzles. Back pressure systems have high sensitivity and versatility, but a lower range than flow systems. Flow system gages require larger volumes of air and nozzles, and are useful where larger measurement ranges are required. Differential, balanced air, single master, or zero setting air gage systems are back pressure systems with a third zero-setting restrictor.


Some air gages are handheld and portable. Others are designed for use on a benchtop or table, or mount on floors or machines. Operators who use benchtop, table-based, and floor-mounted air gages load parts and measure dimensions manually. Automatic gages, such as the inline gages on production lines, perform both functions automatically. In semi-automatic systems, operators load parts manually and gages measure automatically. Typically, machine-mounted gages include test indicators, dial indicator, and or micrometer heads.

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