Plain Plug vs Snap Gauges: When to Use Which

Plain plug gauges and snap gauges both check a plain, non-threaded dimension, but they are built for different jobs.

Plain plug and ring gauges

Plain plug gauges check an internal diameter, such as a bore or hole. Plain ring gauges check an external diameter, such as a shaft. GO members are usually made in tungsten carbide for wear resistance, with NO-GO members in steel, in Reversible or Trilock styles depending on size.

Snap gauges

Snap gauges also check an external diameter, but with a wider contact area and apt contact pressure, built for fast, repeated checking on a production line rather than one-at-a-time bench inspection. GO and NOT-GO can be combined on a single double-ended tool, or set up as a progressive single-ended gauge.

Which one do you need?

If you are checking an internal bore, you need a plain plug gauge. If you are checking an external diameter occasionally or on a small batch, a plain ring gauge works well. If you are checking an external diameter repeatedly at production speed, a snap gauge is usually the better fit.