A locking mechanism for a closure such as a window comprises a body (10) containing a gear wheel (26) that is rotated by a handle (36). This rotation is converted to a locking action by actuating members (23,24) which are provided with a helical thread (25) which engages helical teeth (26a) on the gear wheel (26). Rotation in one sense throws the members (23,24) out of the body to perform a locking action and reverse rotation retracts the members (23,24) into the body (10) in an unlocking action. The position of the members (23,24) can be altered simply by screwing the members into and out of the body.