Hi Mike,
Others are better at this than I am but no one has stepped up yet....sooo.

"the thumbscrew on the top by the "wheel" moves freely." by that I take it you mean screws freely...it likely when tightened stops the shaft from rotating and gradually loosening should allow the shaft varying degrees of rotating....I try and find one with a plastic shaft so that the jaw shaft isn't gowered when rotating.

"The "button" on the top moves freely".... does it have threads? To me it looks like it would be used to adjust the width of the jaw slit to just accept the hook and then the final gripping would be done with what you are calling the "thumbscrew".
But it seems odd to me that what you call the "button" is pushed and not screwed so it holds in one spot????

It'll be interesting to hear from others.