DK45 Models Curiosity

[ritcheyvs]

I was wondering if one of the old heads could explain the differences between the various DK45 models. I have a 45S (shuttle shift) and I see there is a plain DK45, a DK45SE, 45SE HST, and maybe others. This is mainly curiosity on my part but understanding this will also help make sense of other TBN posts. Presumably, the same breakdown applies to other DK sizes.