Taper pin

They are steel rods with one end having a slightly larger diameter than the other.

Some taper pins have a male screw thread on the small end that is designed to project through the hole and retain the pin with a washer and a nut.

Metric taper reamers are designated by the small diameter.

[3] A form of taper pin that precedes these standards is the clock pin, used to accurately and repeatably register parts of a clock to one another.

The size or gauge is defined by diameter at each end, and the length.