Comments for others reading this thread and considering these types of vise.
One may well only have a two hold-down option if the table is imperial – unless one makes off-set clamps.🙂
I bought the type ll vises as sold by ARC. These have slots along the length of the vise and can accommode more clamps if felt necessary (my tables are imperial).
I always use two on one side and one on the other (at least) on my three T-Slotted table and two on each side on the Centec as it only has two T-slots. Belt and braces, probably – but better more than too few.🙂
It costs naff-all to make extras, in both materials and time, when making them as a batch. I think I have about ten clamps – mostly made from scrap. The others (if I can find them) are always available if/when I drop one behind a machine.
The ones not in use with a vise have come in handy once, so far, for holding down a ~10mm part.
Journeyman's type may not be so useful elsewhere.
Journeyman's option for fixings is, IMO, the better option – as long as the countersunk set screws are the correct length for the job. With mine, I can use hex or Allen head, as the height will not interfere with parts held in the vise. I would have gone countersunk cap heads if clamp height was an issue. I leave the T-nut and bolt with the clamp, so they don’t get separated, if possible.
Journeyman’s fixings are closer to the vise than mine (with hex heads), so marginally better clamping force.