DoubleStar ACE Folding Stock Mechanism (FSM) with Boss

The FSM is the standard Folding Stock Mechanism. It fits between the Receiver Block and Modular Stock. The FSM can be mounted to fold either left or right. Will add .75 to your LOP and weighs 3.5 oz.The FSM is manufactured with and without the Boss. The Boss is the raised (oblong shaped) portion on the Arm (small side). Note: If you are ordering a receiver block with your folding stock mechanism we recommend you use an FSM with a boss.