CNC Stainless Steel/Aluminum Spring Guide Thru-Hole is specifically designed for Bolt Recoil Shock System (BRSS) to keep the spring in line and allow the spring to rotate on shaft during high compression. This Spring Guide Thru-Hole is machined with a 6.8mm through hole on stainless steel hub to allow the pushrod to go through thrust bearing and spring guide without any restriction. The Spring Guide Thru-Hole is also equipped thrust ball bearing to reduce spring stress and breakage during high speed spring compression. Made of Stainless Steel and Aluminum.