Jensen's 40mm Cuff ISU Rifle Sm LHS (122L) ISSF Legal This self centering sling has been designed to provide even loading of the arm cuff on both sides without timely adjustments and repositioning of the cuff. With a properly fitting sling, the sling strap can move back and forth on the cuff strap and center itself without any repositioning by the shooter. How to determine size: Bare arm or with T shirt only, measure the arm diameter bent 90 deg. at the elbow and in the upper biceps area. For all leather slings: 11.5 inches dia. = size small 12.5 inches dia. = size medium 13.5 inches dia. = size large For all synthetic slings: 10.5 inches dia. = size small 11.5 inches dia. = size medium 12.5 inches dia. = size large The slings are designed to account for the bulk of a heavy shooting jacket plus at least 1 sweat shirt underneath but DO NOT wear these items when measuring the arm.