The Carbon Reinforced N-04/T-04 Units produced by Tamiya, is classified in Mini 4WD / Kids - Mini 4WD Spare Parts - Chassis Set These units are made with a highly durable carbon reinforced nylon resin. The bearing parts are made with separate parts allowing you to choose from normal tread, wide tread, and normal tread with 520 ball bearing specifications. N-04 Unit x1 T-04 Unit x1 Comes with a choice of 3 types of bearing part. Small parts for attachment included. Compatible with MS Chassis machines.