If your landmine rack attachment didn't come with a spacer, it will tend to rub against your rack during use, stripping the finish off of both parts.
These spacers sit between the metal parts and provide a low-friction surface for the moving parts to slide against.
They come in two sizes - the Monster Lite (5/8") pin size, and the Monster (1") pin size. The 1" are 20mm thick, and the 5/8" are 8mm thick.
Sold individually.