A conventional locking and bolting mechanism is shown in FIG. 1 and may comprise a bolt which is thrown by a handle to secure a door or leaf. The handle may be turned to retract the bolt and release the door or leaf. The handle may be locked by a key cylinder to prevent turning of the handle and thereby maintain the bolt in the thrown position securing the door.
Attacks on such bolting mechanisms may attempt to release the bolt by applying excess torque to the handle. The attacker hopes the excess torque will break the key cylinder and allow the handle to turn and retract the bolt. There are many techniques it is possible to employ to prevent the bolt being released in this way. However, the torque applied by the attacker may damage the handle or other parts of the bolting mechanism. If damaged it may be necessary to replace some or all of the bolting mechanism. To address this problem and prevent damage to the bolting mechanism a conventional solution is to include in the handle pre-weakened or frangible sections such that under excess torque the handle breaks along the pre-weakened sections. However, for the bolting mechanism to become operational again the handle must be replaced. This may take time and will incur costs. U.S. Pat. No. 6,527,314 describes a clutch handle apparatus for opening doors and the like, and includes a torque limiting clutch subassembly which selectively disengages a pin from a spindle to prevent damage. However, the clutch handle described therein is bulky and special techniques may be required to prevent damage to the pin.