These are Tamiya Aluminum 5mm wheel hexes used in many of Tamiya's RC on-road cars. They replace the standard plastic hub found in stock kits. A slit is provided in the wheel hub, and the gap is tightened with a cap screw. This method of attachment more securely fixes the wheel axle to the hub thereby avoiding accidentally dropping the 2x10mm stainless steel shaft when removing the wheel. Furthermore, because it is made of aluminum, it is extremely lightweight and rigid for more accuracy and precision. Available in 4mm, 5mm and 6mm widths to give you different offset wheel options and tuning possibilities! Package includes four Clamping wheel hexes with five pins and five screws.