https://www.gobilda.com/intake-roller-wheel-8mm-rex-12mm-diameter-16mm-width-30a-durometer-8-pack/

This 12mm OD super grippy roller stretches over an 8mm REX® shaft. It is a key component when you are creating a compact intake. This 8 pack covers 128mm of continuous linear shaft. Note: When installed over an 8mm REX Shaft, the outside diameter will be approximately 13mm.