This Bearing Support Spacer fits between the Bearings, alongside the O-Ring when fitting Bearings into a TRAMPA hub when mounting the wheel onto 9.525 & 12mm Axles.
Over time, during the usage of your board, bearings & spacers are put under a lot of force. Ultimately this force has to go somewhere. The Bearings use a Steel ring in their assembly where as the Bearing Support Spacers are made from Aluminum - & when forced against each other the aluminum will lose every time! This is what happens to your spacers between the bearings, & over time the spacers shrink, resulting in an annoying rattle. That's when you fit these spacers!
Important: This spacer will not fit between the bearings of the Superstar wheel because of tolerance issues in the accuracy of the spokes for the superstar hubs - for the Superstar hubs you need 17.8mm spacers