Build a winding desktop marble run and enjoy watching the steel balls run through it! Our 20 piece marble run features a screw elevator to lift your balls back to the top, a turning wheel, and a flip-flop device that makes your marble maze endlessly fun to play with as all 5 mini balls run together in unison! Clip the pieces together with easy to follow instructions and insert the batteries to operate! Requires 2 AA batteries, not included. 3" x 3". Ages 8 . Instructions included.