A wheel pack refers to a set of wheels inside a dial-based combination lock used to verify that the correct combination has been entered. Wheel packs can be found in dial-based safe locks and combination padlocks.
Principles of operation
The number of wheels in the wheel pack directly corresponds to the number of entries in the combination. A three wheel combination lock requires the user to enter three numbers in the combination to set all the components to the correct position and unlock the lock.
Each wheel in the wheel pack has a "true gate"; a portion of the wheel removed where the fence or other mechanism can fall into when the correct combination is entered. Wheels in some medium-high security locks may also include false gates, serrations, or other anti-manipulation features. Wheels in the wheel pack are directly connected to the dial via a spindle and a cam; an additional component on the end of the wheel pack responsible for actuating the bolt via the fence when the correct combination is entered.
Wheels are traditionally made of metal, but higher security safe locks use plastic wheels to frustrate radiological attacks.
Many modern combination lock wheels use a sandwich design that layers 3-4 layers together such that the internal layers can disconnect and rotate, allowing the combination to be reprogrammed by the user via the use of a change key.
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