iOptron 3305 SkyTracker Ball Head (Black) Designed for users to mount and remove camera and lens quickly. Large aluminum alloy ball (1.5 inches, 39mm in diameter) provides super smooth movement and super strong grip The safety stops on the quick release plate prohibit your camera from accidentally slipping out of the quick release adapter (easily be removed with a hex wrench if desired Screw size: 1/4 inch for camera; 3/8 inch for tripods Other features include: maximum load of 11 lbs (5kg), integrated level indicator, compact design at 3.75 inches high.