This is a set of optional parts for Mini 4WD car models.
From the manufacturer:
This set includes two each of 5 different length spacers, in stylish green anodized aluminum. Great for adjusting setup of rollers, rear stay, brake, etc. Diameter: 4mm (outer); 2.1mm (inner)
Compatible Cars: All Mini 4WD and Mini 4WD PRO Chassis cars