There are two options for the bottom ring: The STANDARD BOTTOM RING with six mounting screw holes. This mounts on Heil, Knappco, Fruehauf and Butler. Or the BETTS BOTTOM RING with 12 mounting screw holes. This only mounts on a Betts weld ring.
The most noticeable changes have been the Air Cylinder and Control Box. All improvements allow compatibility with older units and the ability to mix and match components.