Al, I do understand. The reasoning for the milled slot was for slight cg adjustments. The reasoning behind the single bolt hole was that it could possibly provide some resistance to prop breakage. As it was explained to me it could also prevent the rear bearing from popping out in a hard nose dive which could damage several internals including the case. Once the desired position of the mount has been achieved, drilling a through hole shouldn't be a difficult task if desired. I found on one of my planes I used the mount on, I used two small pieces of sandpaper glued back to back under the beams. This worked quite well. Ken