CNC Machined From Aluminium 6061 Wheel Description: (4") diameter Track Wheel: Each wheel is CNC machined and fitted with three 1/2" bearings. (Heavy duty 6201-1/2 RS bearings) Bearings are rubber sealed to protect from dust.Bearings are placed back to back (best combination). A 3/8" wide standoff (sleeve) will raise the wheel of the mounting plate. This bearing combination is the best tested solution against bearing failure as it allow for tighteningThe mounting bolts without causing any axial force on the bearings (ball bearings should not bear lateral load)