Hex Gages - You'll Want to Keep This Reference Handy


Different applications require different types and varieties of tools to ensure the precision and accuracy of measurements. Hex gages are special tools that are used for the inspection of the wrench openings and spark plug wrench openings. Hex gages are essential if you want to measure or inspect machine head fasteners; moreover, they are used for ensuring that the hexagonal holes of parts or workpieces have been machined properly.

More on Hex Gages

Hex gages are manufactured from oil-hardened tools steel with HRC above 60. Also, Hex Gages, both GO and NOGO are manufactured to ANSI/ASME B107.17M specifications within metric sizes from .70mm to 75.00mm and fractional sizes from .028" to 3.00". Hex Gages inspect wrench openings for both, inch and metric sizes. The dimensional data covered in the stated standard includes data for;

  • Spline socket cap screws
  • Different types of hexagons
  • Set screws
  • Shoulder screws
  • Hexagons, and
  • Spline keys are recognized as American Standard

All the aforementioned Hex gages are made with absolute precision and are ideal for measuring/inspecting machine head fasteners. You will find that majority of Hex Gages, if manufactured by quality manufacturers like WESTport Corporation, comes with a certification of accuracy and are also NIST traceable. WESTport Corporation also provides custom Hex Gages that are built as per the specifications of the customers. This includes gages with extra length, tighter tolerances, the use of alternative materials, and extensions.

In particular, the WESTport Hex Gages are made with 60/62 HRC tool steel with long-form calibration services also available.  As for their application, they are used to gage hexagon sockets that are or aren’t chamfered as per the ANSI/ASME B107.17M or ASME B18.3. The gage has two sides or members, GO and NOGO sides. The GO side should be able to freely enter to the minimum key engagement depth that is specified in the standard. The NOGO side should not be able to enter the key engagement depth.

Contrary to the rotary broaches, there is no taper on the Hex Gages. This is why they are held to tight tolerances. The gages are hand-held and inspected the following way: 

  • If the GOgage goes inside the hole perfectly, then the workpiece passes inspection
  • If the GOgage can not go inside the hole altogether, then the workpiece fails inspection
  • If the NOGO gage goes inside the hole, then the workpiece fails inspection
  • In the NOGOgage does not goes inside the hole, then the workpiece passes inspection


The WESTport team has been delivering precision quality gages worldwide since 1989. In putting the needs of our customers first, we are committed to continuously improving our products, processes and services to maintain our position as a global leader in our industry. We are also an ISO 9001, ISO 6508, ISO 6506, and ISO/IEC 17025 accredited manufacturer providing service to over 125 countires with “Quality you can Trust”.