Luth-AR Buffer Retainer w/ Spring - 10 pack. This retainer slips onto the bolt carrier and helps prevent the bolt from coming off while the bolt is being removed. All that is required is the insertion of the set screw. Since the bolt must leave the bottom of the bolt housing the bolt retainer must be inserted from the rear in order to engage the bolt hold open. After engaging the bolt hold open rotate the handle to make sure the buffer is properly seated into the bolt hold open. Specifications for Luth-AR Buffer Retainer: Manufacturer: Luth-AR Color: Black Finish: Manganese Phosphate Features of Luth-AR Buffer Retainer Mil-Spec Manganese phosphate finish Diameter .247 Package Contents: Luth-AR Buffer Retainer Luth-AR LR-01A-10: Buffer Retainer w/ Spring - 10 pack