metalmuncher it looks like you have a handle on it, however most things unless they need to fit someone else's previously made items are pretty much up to the maker's requirements as to size
Marv does a lot of model making therefore his tools are sized relative to his needs C-bag sees something then duplicates it as per his requirements and has come up with some really good mods to tools others have made. I rarely use fasteners smaller than 3/8 16 and most usually 5/8 11 or larger some of my projects might weigh in at several tons while most folks projects will fit in the palm of my hands.
That being said there have been times when even the smallest tools made here such as this lantern vice would be a bit on the largish side when I am repairing or making parts for an old revolver or rifle which I haven't done in quite a while