Machine Design
Allen bolts are

Self locking bolts
Designed for shock load
Used in aircraft application
Provided with hexagonal depression in head

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Machine Design
A bolt

Has a head on one end and a nut fitted to the other
Is provided with pointed threads
Has head at one end and other end fits into a tapped hole in the other part to be joined
Has both the ends threaded

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Machine Design
A hollow saddle key is

A taper key which fits in a key way of the hub and is flat on the shaft
Provided in pairs at right angles and each key is to withstand torsion in one direction only
A taper key which fits half in the key way of hub and half in the key way of shaft
A taper key which fits in a key way of the hub and the bottom of the key is shaped to fit the curved surface of the shaft

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