speed washer

thingiverse

They call it a "speed washer", and you'll usually find one on the outside of skateboard bearings - one on each side. It helps create a solid connection between the bearing's inner race and its cover, preventing friction from building up when the truck or nut is in use. It's incredibly thin and compact, designed not to interfere with the spacing at all. These washers also work really well for fidget spinners - especially if your spinner caps don't come equipped with a built-in spacer. Some do, but others don't. Given its tiny size, it's essential to focus on bed adhesion when printing this part. I use PLA on glass, along with some PVA glue stick.