Bearings should always have a spacer between them and a washer either side. Hangar-washer-bearing-spacer-bearing-washer-nut. No exceptions. That setup helps keep the whole wheel straight, reduces movement on the axle, and stops the bearings rubbing against things as they spin. That means your bearings stay smoother and run faster for longer; not using spacers and washers means you’re just going to need to buy new bearings sooner.
(…really, now we think about it, maybe we shouldn’t be telling you this. Hm.)
Some bearings (like Biltins) have the spacers built in (which is how they got the name). Others, like Synopsis’ Blue Rays, come with bearing spacers included in the pack. But if your bearings didn’t come with spacers – or if you just lost them at some point – this pack of 10mm bearing spacers from Khiro will help keep everything solid on the axle, no matter how much abuse you pile on your wheels. And because they’re aluminium, they should last forever. Just swap them from one set of wheels to the next!
(Note we do also recommend using a proper bearing press to avoid damaging the bearings when installing or removing them, too!)