Whirlwind RMH-100 Rack Hardware Kit

The RMH-100 is a bag of 100 black 10-32 by 3/4 in. screws with nylon washers, for mounting equipment in a standard 19 in. rack. The washers are non-isolating, so the chassis stays bonded to the rack rail rather than being floated off it.

Their other job is cosmetic and it matters more than it sounds: the washer sits between the screw head and the faceplate, which is what stops a rack of gear collecting a ring of scratches around every mounting hole.