Air gaging : High precision measurement technology

The best method to measure diameters with a very high precision  


Air gaging is an old and proven technique of non-contact measurement for measuring with very high precision all kinds of dimensions on precision mechanical parts, but it is especially adapted for diameters with tigh tolerances


Metro has modernized this measurement technique by making it more efficient and accessible, making it very useful in precision mechanics factories.


The largest field of application is on the measurement of external diameters (measurement with a pneumatic ring gauge) or internal diameters (measurement with an air plug gauge), but it is also possible to measure tapers, flatness, etc.


Air gaging is ideal for controlling large series of parts (automotive sector for example) or parts with high added value (aeronautics, medical, defense)


It is possible to measure diameters between 0.8mm and up to 130mm or more.


air gage for small diameter

Measuring 1mm inside diameter on a miniature ball bearing part


The air plugs  or rings can measure 1 or more diameters simultaneously.



air gage

Example of an air gage to measure 14 internal diameters 20.5mm, on 7 altitudes


mesure de 2 diamètre extérieurs par bague pneumatique

Example of measurement of 2 outer diameters on a pneumatic ring


mesure de 6 diamètres sur une pièce d'injecteur essence

Measurement of 6 internal diameters on an injector part



Our systems are capable of measuring mechanical tolerances between 1µm and 100µm or more


Metro air gage systems can achieve excellent repeatability, down to 0.02µm on certain demanding applications (injector parts for example).


Metro can provide you with a complete solution: air ring or air plug gage + associated display and accessories (adapted pressure regulator, pipes, masters, certificates).


air gage for internal diameter

Measuring station for 8 internal diameters on 3 steps



Air gage measurement station


Metro can provide measuring stations with all needed elements attached on a compact fixture. M-Bus modules and regulator are attached on the rear side


Pneumatic measuring systems can be used directly in the workshop, and are not very sensitive to the cleanliness of the parts, which gives a great advantage over optical measuring systems which require an irreproachable part cleanliness during the measurement.


measure sur rectif sunnen

Manual measuring station for an internal diameter directly in a Sunnen machine with a very oily environment.


Manual measuring systems are very easy to use and generate operator independent measurements


We also supply systems to be installed on automated machines (floating mounting), combined with a  Profinet or a Modbus PLC communication.


machine automatique de tri avec tampon pneumatiques

logo profinet

Automatic sorting machine (being assembled) measuring 4 diameters out of 7 part references, ie 28 possible diameters. The Metro M400 display communicates in Profinet with the main PLC managing the machine.

Technical specifications


The large majority of air gages are unique parts made on demand according to your needs.


Here is a non-exhaustive list of possibilities:


  • Masters : our systems require calibration with 2 masters (mini and maxi). We supply the masters adapted to the air gage ordered, with an accredited certificate on request
  • TICN Coating : Physical deposition of a layer of titanium carbonitride. The hardness of the coating is extremely high (3000 HV) for a coating thickness of 2 to 3 microns. The mauve gray / blue gray color characterizes this coating. The interest lies in the very high resistance to wear and a reduction in the coefficient of friction.

TICN-Coated air gage and its masters


  • By-pass nozzle (integrated restrictor) This technique allows a stabilization time up to 5 times faster than a conventional air gage. This also makes the air gage exchangeable without adjustment on the Metro display. Finally, the absence of air circulation in the electronics increases the life of the device by the absence of possible pollution (dust, oil, water).
  • Mounting on table base or handle

  • Air gage mounted on a handle


    Double pneumatic ring with "vee" guide of the part and push button to take it out


  • Floating and / or anti-penetrating mounting for automated machine mounting. Since the play between the air gage and the part is very low, it is often necessary to use a floating system to ensure proper insertion of the part into the buffer. Different solutions are possible depending on your project and your machine environment
  • Measuring fixture combined with air gage and inductive probes : we can combine inductive probes with an air gauge to take for example a height dimension or a groove diameter not measurable by air.
  • Number of nozzles per level : Most air gages have two nozzles at 180 ° per measurement level. A static measurement will show the diameter at a given position. By turning the part you will be able to obtain an out-of-roundness defect.
    It is also possible to manufacture the air gage with 3 nozzles at 120 ° per level and thus be able to detect a triangulation defect during a dynamic measurement. 4 or more nozzles will make it possible for example to obtain an average value, for example if it is not possible to orientate the part. We can also supply double lips leakage air gages to achieve an extremely repeatable average diameter.
  • Taper measurement Many tapered parts are checked using pneumatic measurement. Metro has a solid experience in the measurement of medical parts (cone measurement on dental implants, hip or knee prosthesis), but also HSK machine cones etc. A taper air gage or ring generally has 2 or 3 diameter measurements and a taper calculation is then performed in the display. It is possible to deduce other parameters such as the theoretical diameter at the gauge plane, the straightness of the cone, etc. We can display the angle of the cone in decimal degrees or DMS (Degrees / Minutes / Seconds)


Displays and interfaces


Metro manufactures electronics to operate air gages


Thanks to our design, our system can adapt to all brands of air gages with at least the same performance as the original system



Retrofit of a Mercer system, we kept the air ring and plus gage and installed an M3 display



Retrofit of an Etamic system, we kept the air plug gages and installed an M3 display



Retrofit of an EL-Jet membrane system from PFL + inductive sensors by M-BUS MB-AG modules for operation on an M400 display





Send us the drawing of your part with the dimensions to be checked and we will send you a proposal. Specify whether the measurement is manual (table or handle mount) or automated, the number of parts to be measured or the cycle time expectations.
After ordering, we will make a drawing that we will have you validate to start manufacturing. We can either provide a air gage to connect to your existing electronics or provide a complete solution with the display.