Telescoping "Snap" Gauges are used to quickly measure the inside of a cylinder. Spring loaded, you put your snap gauge inside of the cylinder, open up the gauge and snap it until it hits the wall. Next, close it off and lock in into that position. Once you have locked the telescoping snap gauge into position you can measure it using either a micrometer or a caliper.
We've been carrying this set of telescoping gauges, also referred to as "snap" gauges, for decades. They are made overseas, but we haven't had complaints about the quality and feel they are a good buy for they person who doesn't feel they can afford to buy a more expensive American or European set of gauges. This is a six piece set that starts at 5/16", goes up to 6", and comes with a handy plastic carrying case that marked with the gauge numbers for ease of use. The numbers are marked large enough so even most people who have poor eyesight can see them clearly.