Telescoping gages (and their little brothers, hole gages) are used to measure bores where inside micrometers will not fit. (Typically holes smaller than 1-1/2".)

  operate like the name implies, one end (or both ends) "telescope" into larger diameter sleeves. These ends are spring loaded and are held in any given location by a long screw that is operated via a knurled ring at the end of the handle. (Small hole gages operate similarly except that the long screw is terminated by a wedge that spreads the split-globe heads apart.)

   Specifications:

Range	mm	8-12.7	12.7-19	19-32	32-54	54-90	90-150
	in
L	mm	102	102	102	127	127	127
	in	4	4	4	5	5	5

 

  Steps   

 

 

Collapse the telescoping gage.

Secure the telescoped gage by turning the knurled ring, lightly tightening it.

Insert the gage into the bore to be measured.

Roughly align the handle parallel to the axis of the bore, and release the knurled ring. A little practice - before measuring - locking and unlocking the ring will give the user a knack for gradually extending the gages tubes against the bore without having them slap vigorously against the bores surfaces.

Lock the knurled ring very lightly, then rocks the gages handle about the bores axis. Properly accomplished, the user will discern a light "drag" on the gage as the lightly-rounded gage ends engage the bores surface at its largest diameter. If no drag is felt, the gage tubes are NOT ninety-degrees to the bores axis and aligned at its largest diameter. The user MUST wiggle the gage handle until this is accomplished.

Tighten the knurled ring a bit more to ensure that the gage ends are held in position for measuring.

Using an outside micrometer or a vernier caliper, rock the telescoping gage until a drag similar to that felt in the bore is felt against the faces of the measuring device