A caliper.
A caliper is a measuring device for finding very precise measurements of an item. These devices are common in many fields, such as mechanical engineering and electronic design. There are three basic forms of this device: exterior, interior, and depth, and each has its own uses and methods. Of these three basic types of tools, there are several types with specific functions for a purpose.
A caliper is a measuring device that consists of two parts that open and close. The opening area can be removed from the item you are measuring and measure itself, allowing non-standard items to be sized quickly and easily. The micrometer version is essentially a very precise gauge; it measures things on a very narrow scale, and often has a built-in readout of the size of the measured object.
Most micrometer calipers have their reading directly on the handle of the instrument. This usually consists of lines that are revealed when the cursor is opened. In addition to these lines, there may be a secondary scale that measures the fractional areas between the lines of the primary scale.
There are three basic shapes. An open cursor measures the outside of an object, such as the head of a screw. An internal gauge measures an opening, such as a screw hole, from the inside. A depth gauge will measure the depth of an opening from the bottom up. Outside of these three basic styles, many tasks have their own gages, including those for measuring threads on a screw and aligning materials inside a milling machine.
There are several methods of making a caliper, but the end result is almost always the same collection of parts. The frame contains the handle and the upper jaw. The anvil sits in the upper jaw of the collet and provides a flat, solid surface for the material to rest on. The spindle is the screw that goes up and down the other side of the anvil – it does the actual measurement. The sleeve is at the bottom of the shaft and reads the actual size of the gauge opening.
The gauge measurement reading on the sleeve is based on the relative position of the spindle. The axle is on a screw that allows it to move up and down. As the spindle moves, the rotating screw creates a mechanical change in the spindle. The spindle separates when the screw retracts and condenses when the screw comes out. This means that the axis always displays the aperture size using its own printed scale.