YHM Hub Direct Thread Mount System for HUB compatible suppressors. Threads: 1.375-24 (M13.5x1LH). Caliber bore: .45 cal. Material: 17-4PH, Black Oxide finish. Weight: 1.7 oz. To install, remove your existing mount from the suppressor and thread on the HUB Direct Thread Mount using a 3/4 inch wrench, then thread the suppressor onto your barrel.