1/4" (20) Rear Wheel Only = 18x 1/4" (6.35mm) ball bearings. 3/16" (20) Front Wheel Only = 20x 3/16" (4.76mm) ball bearings. 3/16" (22) Front Wheel Only = 22x 3/16" (4.76mm) ball bearings. 3/16" (22) and 1/4" (18) Both Wheels = 22x 3/16" (4.76mm) & 18x (6.35mm) ball bearings.
