A mechanical expansion shell assembly has an expansion shell with a plurality of leaves and a plug with a plurality of sloped surfaces. The inner surfaces of the leaves are positioned in overlying relation with the sloped surfaces of the plug. A friction reducing material is positioned between the overlying surfaces and is arranged to reduce the torque applied to the roof bolt connected to the expansion shell assembly to obtain a preselected lateral force on the expansion shell leaves. In another embodiment, a friction reducing material is positioned between a nut threaded on the roof bolt and the underside of the expansion shell ring portion.