The Armaspec FULCRUM-45(TM) is an ambidextrous 45 degree safety selector for the AR15/AR10 platform. It's set to fire at around the 45 degree point instead of 90 degree to allow for faster disengagement. Its easy to reach levers and incredibly smooth action makes position selection a natural, fluid movement for the operator while having a super crisp lockup, leaving you no doubt about your safety status. Once installed, the FULCRUM-45(TM) operates easily from either side of the receiver for intuitive use in the field by a variety of shooters in any circumstance. Operates exactly as you want it to.The 45 degree side is designed for firearms that have the correct "FIRE" markings on the receiver to match the 45 degree fire position of this safety selector. Do not use on lowers without the 45 degree "FIRE" markings on the receiver. If you have a receiver that does not have the correct markings, you should use the 90 degree side. Pat. Pend.