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What is a Bayonet Mount?

M.J. Casey
M.J. Casey

A bayonet mount is a fast, secure, and precise way to join two pieces of equipment temporarily. This mount employs two or three pins or wedges that are positioned into slots or grooves of another piece. The connection is made with a twist and a compression force of one piece into the other.

This coupling mechanism was first used by the French around the 1670s. Earlier soldiers had discovered the effectiveness of jamming knives into the barrels of their muskets once engaged in close-quarter battles. The disadvantage of the adaption was that the muskets could not be fired until the knives were removed. Gunsmiths set to work on this problem and developed a short tube that fit over the end of the barrel and was locked in place by use of a pin through a zigzag slot. The blade was welded to the side.

Man with a drill
Man with a drill

Peaceful applications of the bayonet mount became plentiful with the development of manufacturing standards and engineering drawings with matched tolerances for connecting equipment. They are commonly used in camera equipment to attach a removable lens to the camera body. The precision alignment of the tight–tolerance pieces ensures the face of the lens is parallel to the camera body, avoiding distortion of the picture.

Some hand tools employ a bayonet mount for ease of use. Drivers may use several different tools that are quickly switched. The bayonet mount works well in rotating tools such as drills because the force of the rotation of the locked piece is aligned with the force to lock the device. The circular motion reinforces the mount. The tight grip of the bayonet mount is also essential in tools to avoid wobble when in use.

Bayonet mounts are not restricted to metal applications. Plastic uses include certain audio, video, or data connections. These pieces fit inside one another and then twist and lock together. The bayonet mount casing may be made tight enough to exclude water and dust.

The strength of the bayonet mount is equal to the shear force just before breakage of one or more of the pins. The shear force would be applied perpendicularly to the direction of the mount. The ability of the connection to withstand being pulled apart by opposing forces is high, as the slot is designed to provide significant resistance in the opposite position. The pieces have to be pushed together before a sideways force will successfully untwist the connector.

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    • Man with a drill
      Man with a drill