Machine Design and Shop Practice Exam 2026 – Complete Preparation Guide

Torque is transmitted through the contact between the key and the mating surfaces in a shaft–hub joint. A flat saddle key is designed so the key sits in a saddle-shaped groove and is pressed between surfaces, creating a strong frictional grip over a larger contact area. This friction resists rotation, so the key’s ability to transmit torque relies mainly on friction rather than the key being sheared along a single plane. Other key types depend more on the shear strength of the key or on specific locking features, not on frictional grip, so they don’t rely primarily on friction to transmit torque.