Presma Stabilizing Fin for AR Pistols 223/5.56/.308 Black. If desired a standard sling may be wrapped around the Fin and forearm further stabilizing the pistol to the forearm in both horizontal and vertical planes. This high-strength polymer product fits all pistols equipped with a standard AR pistol buffer tube (1.25in in diameter) for a secure worry-free fit. The Stabilizing Fin is a lightweight clamp-on ergonomic AR pistol enhancement and acts as a forearm buttress. Does not fit adjustable tubes (Mil-Spec/Commercial) or A2 rifle tubes. U.S. Patent D897480 Specifications for Presma AR Pistol Stabilizing Fin: Manufacturer: Presma Color: Black Gun Type: Rifle Stock/Brace Material: Polymer Condition: New Package Contents: Presma AR Pistol Stabilizing Fin Screw Allen wrench Presma AAST18: Stabilizing Fin for AR Pistols 223/5.56/.308 Black