smooth is part of:

smooth contains:

Full expansion for smooth:
   100%  Small Smooth Tires from 6444, no hubs
   100%  Small Tiny-Peg Hub w/ Thin Tires
   100%  Small Tiny-Peg Hub w/ WideFlat Tires
   100%  3x3 Rubber Tire for Technic Pulley
   100%  3x3 Technic Pulley w/ Tires
    90%  2x2 Disc w/ Convex Round Bottom