Bore gauge is a convenient term for the measuring or transfer tools that are used in the process of accurately measuring holes.It is very extensive, with products available for a broad range of applications. Some are available with interchangeable measuring heads for different diameters or extensions for depth. They can have electronic displays micrometer-type vernier scales or a dial indicator.
Dial Bore gauge is a special tool, which is used to accurately measure the inside diameter of a hole, cylinder or pipe. In conjunction with a micrometer, a bore gauge will give you the exact reading of a bore size. A typical bore gauge is comprised of a shaft with a dial indicator at the top and a measuring sled at the base. The measuring sled consists of three guides and an actuating plunger. Dial bore gauges give you quick and accurate readings on the size, less than perfect roundness or wear.
Bore gauges are the 1st choice for fast measuring / gauging of hole diameters. The benefit of a bore gauge over a 3 point internal micrometer is that is offers a faster and more cost effective way of measuring or gauging hole diameters as one tool can be used for a wider range of diameters. The downside to bore gauging compared to micrometers is that it is not as accurate as it is often only measuring over 2 points.