The Swivel & Lock System allows stirrup to be rotated 360 degrees or to be locked into any position for maximum comfort. It also allows the fender to lay flat against the rider's leg. Guaranteed to relieve knee and ankle strain. Simple saddle installation. To Determine What Size Swivel & Lock System is Needed, Measure the Width of the Stirrup Neck (Top of the Stirrup where the Fender/Stirrup Leather Attaches).