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