the basic Bill Davis Custom had a 1" diameter bull barrel with a sight rib above and a lower rib...i think hat was call their Level III
the Level IV added a heavier lower rib, which extended lower down below the barrel...like a slab sided L-frame
the Windmaster had the same weight as the Level IV, but they built the weight into the barrel, so there would be less surface area for the wind to affect if it was blowing from the side (cross wind)