I have seen a lot of hook clamps. Some were not Doughty and the not-Doughy ones felt flimsy, or there was a little wing bolt on the top fastener, or worse, a hex-head. Some other designs have a threaded bottom hole, which I find to be the opposite of helpful; this one has a clearance hole.
When buying a new hook clamp, it's nearly always for a new fixture. I genuinely can not remember ever replacing one. The only time I can remember fastening a hook clamp to an old fixture is when it had temporarily been used on a floor stand, and in that case I've kept the fixings in a safe logical place (usually!).
I do keep a ready stock of fixings but far simpler if the hook clamps are supplied with the necessaries.
If you have something really heavy or awkward to hang, there are other designs to solve your problem. For me, the vast majority of fixtures are not awkward to handle and are well within the 40 kg limit of the Doughty T20104. In these circumstances, there is only one alternative: Doughty T2010401, which is the same model but in black.