lock mechanism, it forces apart the lever arms, which then permits the wheel center to rotate freely. This in turn allows the owner to set a custom combination. Additional security Some rotary combination locks include internal relockers or relocking devices that separately lock the shackle or bolt when an attack is detected, including mechanical levers that respond to attempts to dislodge the locking mechanism ("punching"), thermal (fusible) links that melt in response to a cutting attempt, or tempered glass that breaks in response to a drilling attempt. Wheels may be made of radiotransparent materials such as Nylon, Lexan, or Delrin to prevent the use of X-ray imaging to determine the wheel position and required combination. See also Combination lock Safes References External links How rotary combination locks work, HowStuffWorks Locraker - Automatic combination lock cracker, Neil Fraser, 13 March 2002 - rotary combination lock cracking machine - contains a detailed description, with photographs, of rotary combination locks and their security concerns Locks (security device)