These are Lightweight Treaded Wheels by Du-Bro.

FEATURES: Lighweight
          Shock Absorbing
          Fits inside most Wheels Pans and Retracts
          Grey Eight Spoke Hub Design

INCLUDES: Two Wheel

REQUIRES: Nothing

SPECS:    Diameter:     45 mm (1.75")
          Hub Diameter: 3 mm (0.125")
          Width:        16.25 mm (.640")