Aluminum Hex Tread Spacers (Black) 0.5 mm, 1.0 mm [Yokomo] ZS-011TSB These are super precise wheel hub spacers. It is an aluminum spacer for adjusting the tread width by clamping it with the wheel hub when installing the wheel. Each shim of 0.5 mm and 1 mm thick is included, each of which can be used according to the situation. Includes: 2 x .5mm hex hub spacers, 2 x 1.0mm hex hub spacers