Save money For ATVs, dirt bikes, & go-karts Easy DIY repair Allows precise chain lengths 420 chain master link for scooters, motorcycles, dirt bikes, go-karts, and ATVs Master links are used to connect each end of an open loop to create a closed loop chain (also known as a fixed length chain) 420 chain master link for scooters, motorcycles, dirt bikes, go-karts, and ATVs. Master links are used to connect each end of an open loop to create a closed loop chain (also known as a fixed length chain). You can also use a master link to repair chains with a busted link – just remove the bad link and replace it with a master link.