The Barrel Bushing Lock Spring is located inside the FSB (Front Sight base) on your AK47 behind the Barrel Bushing Lock. This spring pushes the bushing lock forward to hold the AK slant muzzle break (PolyTech AKS-762) or muzzle nut (PolyTech AK47/S Legend Series) in place. To install, remove the muzzle break and take out the FSB (Front Sight Base) pin. Remove the bushing lock and replace the spring with this original Chinese PolyTech part. It is best practice to install a new Bushing Lock (item# 70-01-37) while you have your AK47 Muzzle Break disassembled.