The snap gauge compares the outside diameters of parts such as shafts and journals to a standard. It can compare diameters from zero to 8 inches at an accuracy of 0.0001 inch. Figure 2-5 shows a typical snap gauge. Most snap gauges consist of a frame with an insulated handle, a hex wrench mounted in the handle, dial indicator digits calibrated in 0.00l-inch divisions, a bezel clamp, adjustment wheels, locking wheels, a backstop, a lower anvil, an upper anvil, and a guard. Whenever you use a snap gauge, use the handle and avoid touching the gauge proper because body heat may affect the reading. For the same reason, handle the standard plugs only by their plastic end. Clean the anvils and the backstop with a clean cloth. To use the snap gauge, follow the manufacturers operating instructions. After you record the readings and compare the readings with the design specifications, clean and store the snap gauge in its appropriate storage location.

Figure 2-5.Typical snap gauge.