The lower bushings are roughly 1.45 inch diameter to fit in the 1.5 inch hooks. There are straight bushings to fit the clevis style and the shoulder type that are turned down from about 2 inches on the ends to the 1.45 inches for the single hitch pins. These pins are cat 3 lower size.
The top link bushings are cat 3 pin size and I have found a few bushings that go from cat 1 to cat 3. Most of the time I have to use two bushings a cat 1 to cat 2 and slip a cat 2 to cat 3 bushing over it. For some implements I use cat 3 solid pins and weld them in place, cutting to fit the implement. The last is what I prefer since it is hard to loose one that is welded in place and it eliminates the need for the often found piece of flat bar that is in the way.