Rigid couplings connect rotating members such as shafts and transmit torque and motion. Most rigid couplings are made of aluminum, steel, or stainless steel. There are several basic types of products. One-piece set screw devices are solid, O-shaped couplings that attach to shafts with set screws. One-piece clamp couplings are solid, C-shaped devices with a split that is closed with tightening screws. Two-piece clamps are split axially into two pieces, each of which is closed onto the shaft with tightening screws. Multi-screw couplings are commonly available. Typically, all of the screws are inserted from the same direction. Shrink discs are rigid couplings with two external rings that tighten together axially and exert inward force on a third ring via tapered surfaces. This closes the inner ring onto the shafts and provides a secure connection. Rigid couplings with keyways include keys that can be used to stop the rotation of the shaft couplings.