An expansion shell assembly for mine roof bolts includes an expansion member threaded onto an associated mine roof bolt. A support device is annularly disposed around the associated roof bolt. An expansion shell is annularly disposed around the associated roof bolt between the expansion member and the support device. The expansion shell has a base ring for engaging the support device and fingers for engaging a peripheral edge of the tapered plug. The engagement between the base ring and the support device permits axial traverse movement of the support device relative to the expansion shell for tensioning the roof bolt.