Like new Slik U700 Universal Dolly Wheels Very smooth moves.
It folds all 3 wheel segments in one direction when not in use, and it raises any tripod/camera kit weighing up to 33 lbs (15kg) 6.1" off the ground with 3" rubber wheels. The tripod's feet are allowed a maximum diameter of 40.2" (102cm).
Construction is all metal, and the U-702 is meant to provide quick and smooth movement of your tripod and camera in a studio environment, or anywhere else where you're shooting on a continuous hard and flat surface.