=Introduction= In mechanical engineering, a key is a machine element used to connect a rotating machine element to a shaft. The key prevents relative rotation between the two parts and may enable torque transmission. For a key to function, the shaft and rotating machine element must have a keyway and a keyseat, which is a slot and pocket in which the key fits. The whole system is called a keyed joint. A keyed joint may allow relative axial movement between the parts.
Commonly keyed components include gears, pulleys, shaft couplers, and washers.
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=References= * [https://en.wikipedia.org/wiki/Key_(engineering) Key (engineering)] * [https://www.surpluscenter.com/Power-Transmission/Shafting/Key-Stock/1-4-Square-Key-1-5-Long-G-G-Mfg-411-0424-1-5030-25-A.axd 1/4“ square key]