12.7/19.1 that is 1/2”-3/4” clamps, 1/2”-3/4” refers to the size of quick release joints, there are two kinds of chucks corresponding to this kind of quick release joints, 25 and 50.5 respectively; there are also two kinds of corresponding slots, 8mm and 9mm.
In addition, the basic connection method of clamps are stacking type and the middle of the clip, the middle of the clip is more. Both of these do not affect the use. The following chart:
There are four basic types of nuts for clamps. a kind of bias, these four do not affect the use. The following chart: