What type of keys are shaped like a half moon?

Woodruff keys are indeed shaped like a half moon, which is a distinctive feature that sets them apart from other types of keys used in machinery and equipment. These keys are designed to fit into a semicircular slot in a shaft, providing a secure connection to a hub, wheel, or gear. The half-moon shape allows the key to provide reliable, even torque transmission while reducing play and misalignment between the components.

This design also enables easier installation and removal compared to other key types. The use of Woodruff keys is common in applications where precise alignment is critical, such as in rotary motion devices. Their unique geometry also aids in maintaining a stable fit under varying loads, making them a preferred choice for many mechanical applications.