One (3") 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 allows for tightening The mounting bolts without causing any axial force on the bearings (ball bearings should not bear lateral load)