This idler sprocket lets you add tension to your 8mm pitch chain in an assembly. It slips onto a 6mm OD standoff, spacer, or shaft. It also fits onto the goBILDA® Arc Slot Tensioner (1524-0001-0001) which lets you dial in the exact amount of tension you need. The built-in shims on either side of this sprocket allow it to be pressed right up against a bearing without binding the inner and outer races or needing a separate shim. The acetal makeup of this part means it will be low-friction with excellent wear characteristics.