Push Button actuated folding mechanism can be made to fold left or right by inverting the mechanism on the receiver block. Body is machined from 6061 T6 Billet aluminum, arm and key from mild steel. Positive lock in the open and closed position. The FSM-PB is manufactured with and without the Boss. The Boss is the raised (oblong shaped) portion on the Arm (small side). If you require one with or without the Boss pleases specify in the Order Instructions section during the checkout process. If you do not specify your order will be shipped based on availability.