The low-cost toggle clamps I see have 4 holes to mount with(photo below). I'd like some with a single threaded stud on the bottom, 1/2-13 or 3/8-16. Any suggestions?
You are going to have to make an adapter plate to stud mount, if that's what you want. Manufacturers of the over center clamps are "Destaco", "Carr-Lane" to get a feel for what is available.