In cone systems the case is machined with tapered bores and the side gears have a mating cone shape on their backside. There is a spring or springs that apply pressure to the side gears causing them to wedge into the case. It also uses spider gears and a cross shaft as above. The operation is much the same as the clutch system, but utilizes tapered cones instead of clutch packs. Standard Duty units have smaller cones than the Heavy Duty. Larger cones have more surface area resulting in more holding power and longer life. These are non- rebuild-able and must be replaced when worn out.