What is a rectangular slot or groove machined down the length of a hole called?

The term for a rectangular slot or groove machined down the length of a hole is known as a keyway. This specific feature is designed to accommodate a key, which is a mechanical fastener used to connect two rotating parts, like a shaft and a gear, in a manner that transmits torque. Keyways are essential in providing a secure and precise connection to prevent relative rotation between these parts.

A keyway's dimensions and shape allow for efficient force distribution, ensuring that the load is handled correctly during operation. This is crucial in applications where accuracy and reliability are necessary, such as in machinery and automotive components. The correct identification of a keyway is important for engineers and machinists when designing and fabricating mechanical systems that require such features.

Other terms like notch, groove, and cutout may describe similar features but differ in their specific applications and definitions within machining and manufacturing contexts. For instance, a notch typically refers to a small cut or indentation and does not necessarily extend down the length of a hole. A groove can refer to a variety of configurations and is not exclusively rectangular or mechanical in nature, while a cutout generally implies a removal of material without the specific intent or mechanical function associated with a keyway.