4" Standard Crank Handle. The RV industry's first redundant safety check system protects you and your camper from mishap or failure. Happijacs camper jacks feature 2 inch square powder coated inner and outer legs which are significantly stronger than jacks using round tubes. Rated per ANSI standards these jacks safely lift an incredible 1500 pounds acme screw to 1900 pounds ball screw per jack! Concave cupped footpads reduce movement and provide maximum stability. They can be easily installed retrofitted onto most campers with Happijacs Z bracket mounting system the industry's strongest most secure bracket system. These amazing jacks are also unique in that they can be easily upgraded from manual hand crank to an electric wireless remote control system with the simple addition of an electric motor drive kit and wiring kit. A quick release feature is also available with the ball screw jacks making it the only electric remote ready jack with a quick release option. All this makes leveling your camper simple quick and stress free.