NOTE: ESF-H1 has a single rear facing QD swivel socket.ESF-H1 (End plate, Sling Adapter, Forward Controls Design, Heavy, 1 socket) is a drop in end plate replacement for the AR platform (both 223 and 308 spec).ESF has rotation limited side facing sockets. The rear facing socket has no limiters, as the receiver extension effectively limits the swivel's rotation.NOTE:End plates that incorporate side facing QD swivel sockets can mask available wrench notches required for torquing. A conventional castle nut wrench has 3 lugs, in some cases, the socket housing may partially block access to one of them. A 2 lug castle nut wrench, such as the AR Multitasker, or our JCW (Joint Castle nut Wrench) would be required to torque the castle nut properly.ESF's receiver extension indexing tab can be tight on some receiver extensions.ESF-H1 (rear socket only) does not have rotation limiters, as the QD sling swivel is prevented from rotating 360 degrees by the receiver extension.