Collar clamps help to reduce the direct loading of the cart on your kayak's bottom / keel. Direct loads on hull bottoms can cause deformation of the kayak. Even loading at scuppers and hull bottom reduces hull-bottom deformation issues. Fits all year-models of Hobie plugin carts. Note: Be certain that the cart inserts clear through the kayak and protrudes into the cockpit / cargo area surface. Kayaks should never be left on carts for prolonged periods of time. * (Standard on Hobie Carts shipped / starting summer 2009)