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How to Read a Telescoping Gage

Telescoping gages, also called bore gages, are used to measure the inner radius of a hole, or bore. A micrometer is used in conjunction with the telescoping gage to determine size and proper fit of screws and bolts. The telescoping gage is spring-loaded and provides better accuracy than most diameter measuring tools of the same kind. The gage consists of a lock screw and two rods that fit into each other and extend when the spring action is activated.

Instructions

- 1
  Turn the lock screw to the left to loosen your gage. The lock screw is located at the top of your gage handle.
- 2
  Lower the telescoping gage into the hole to be measured at a 5 degree angle. Turn the lock screw to the right to lock the springs into place and prevent your gage from moving once you pull it out. Ensure there is no movement whatsoever.
- 3
  Pull your handle to the left and slide up on the gage to remove.
- 4
  Read your measurement with an outside micrometer. Open your micrometer fully by turning the end thimble to your left. Insert your telescoping gage into the center of your micrometer. Turn the thimble to your right until it stops against the gage, then turn the locking lever to hold your position.
- 5
  Read your measurements from the barrel first. Each marking represents 1/2 of a millimeter. Write down your measurements on a piece of paper in decimals. For example, if your reading is halfway between 4 and 5, you would write .45 for your reading. Take the reading from your thimble next to determine the distance. Add both measurements together to find your exact radius.

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