What Is a Telescoping Gauge?
A telescoping gauge is an indirect measuring device, the head of which can be positioned inside holes or openings and then extended to touch the walls. The gauge can then be extracted, and the size of the extended head can be measured with a micrometer or vernier caliper to determine the interior radius of the hole. This is essentially no different from a set of inside calipers, save that the distance which the head extends can be locked after measurement to ensure it's as accurate as possible.
Who Uses Them?
Mechanics most often use telescoping gages, though anybody working with machinery needing to measure the interior radius or calculate the circumference of a hole or pipe can use them to the same effect. They are typically used to measure the interior radius of the bore or cylinder of a crank case in which the cylinder's pistons would extend and retract. For both internal combustion and diesel engines to work properly, absolutely no air can pass out of the cylinder when the piston extends, compressing the combustible gases within. This means that the circumference and radius of the piston head must match the circumference and radius of the cylinder as closely as possible. This means that precision indirect measuring tools such as telescoping gauges are an absolute necessity.
How is a Telescoping Gauge Used Properly?
The process is simple. First the appropriate sized gauge is chosen, as they come in many sizes. The spring drive sides of the head are pressed down in the closed position, and locked into place by means of turning the end of the knurled grip. The head of the gauge is extended into the hole so that the length of the gauge's handle is lying parallel with the hole. The grip is unlocked and the poles are situated at either side of the gauge's head extend, striking the sides of the hole. The lock is then tightened again to ensure that the poles don't extend or retract any further. The gauge is carefully removed, where the distance between the holes at the gauge's head are measured.