Every inline skate wheel needs two bearings AND one spacer between the bearings. You could think that the bearings could be separated by the plastic hub at the inside of the wheel, but this material in plastic is not strong enough to keep the bearings separated during the forces that exist when you propel the skate. That is why you need a spacer between the bearings.
If you doubt whether you need a spacer with a 6 mm or an 8 mm axis, then use this rule of thumb:
- for an inline hockey skate with four wheels, you need the spacers with a 6 mm axis, that are displayed here.
- for all other inline skates (inline hockey skates with three wheels, fitness skates, aggressive skates, freeride skates etc.) you need the spacers with an 8 mm axis, that are displayed on this page: https://www.slidingtiger.eu/home/Bearings?product=PS900421
Spacers are packed per 8, so one pack is suited for one pair of skates.