Calipers

Calibers are devices used to take a measurement of a physical object. There are a few different types of calipers that we will discuss. Dial calipers are the most commonly used instrument in the machine shop and laboratory, but inside and outside calipers also have their place in the tool chest.

Inside Calipers

Inside calipers are used to measure the inner diameter of a part, often a pipe or tube. They are commonly spring loaded with an adjustment nut and two outward facing measurement probes. The user adjusts the caliper until it just drags on the inside diameter that they wish to measure, then uses micrometer, steel rule, or other measuring device to measure the distance between the points of the caliper.

Outside Calipers

Outside calipers are used to measure the outer diameter of parts, such as tubes, pipes, or other semi-uniform parts. The user adjusts the points of the outside caliper until they drag on the surface to be measured. Another measurement device such as a steel rule can be used to measure the distance between the points of the caliper.

Dial Calipers

The dial caliper is the most commonly used measurement instrument in the machine shop or lab. It consists of a sliding carriage on a scale with hardened jaws at the end of the carriage and scale. The coarse measurements, commonly inches and tenths of inches are read off the main scale. A rack and pinion gear system drives a dial to allow measurement easily to the nearest thousandth of an inch. These calipers are also available in digital form. Both styles have a locking mechanism so the user can set a fixed distance and use the hardened points of the caliber as scribes to mark parts. These are easier to read than Vernier calipers, and have become much more common. The dial caliper can be used to measure inside and outside diameters, as well as depths in certain cases.

Vernier Calipers

The Vernier caliper is similar to the dial caliper except that it uses a sliding Vernier scale instead of the dial rack and pinion mechanism. Similar accuracy can be achieved, and Vernier calipers are often found in much larger sizes than dial calipers. As with the dial caliper, Vernier calipers can be used to measure inside and outside diameters.