Stainless Steel Locknut
We source a lot of our stainless steel hardware from outside the bike industry. Often the hardware the comes stock with fenders and racks either rattles loose, or rusts. These nuts are made of aerospace grade stainless steel and will never rust, and have a nylon insert to prevent them from ever coming loose accidentally. M5 has an 8mm wrench surface, M6 has a 10mm.