The size of the pins? Measure the holes afterwards. Having dismantled one of mine recently to fit copper jaws (the screws, 1/4 BSW around 3/4 inch long were very stuck and needed spotting with an end mill, then left hand drilling on the mill with one requiring heat to remove)

The pin holding the nut into the main body at the rear of the vice is somewhere around 3/16", the one on the screw a bit smaller, possibly 5/32", but they could be metric, I never measured and simply refitted the ones I removed.

Besides the slight variation in taper (1:48 &1:50) metric pins are measured at one end, imperial ones at the other and at the moment I can't recall which is which.

Removal? parallel pin punch, hit with a copper & hide mallet, not much force needed at all,

The one on the screw will catch you out if you drive it through too much and jam up the screw and prevent if being turned, so partial drive through, rotate the screw 180 degrees and pull out the pin with a pair of pliers / mole grips etc is the better option.

I would not use a hide or rubber hammer as the probably small head of the punch might leave a dent in it. I would only use a lead/copper/aluminium hammer if the hitting was light for the same reason. I can't really think of a reason not to use a steel hammer when the pin punch is in between to protect the job but would be interested to hear a reason.

Size of the pin punch? a bit smaller than the small side of the taper pin, it also means you have something around the size of the pin to compare with so you don't accidentally hit the wrong end of the pin and possibly make an easy job something else.

Hitting something hard like a pin punch with something hard like a hammer will indeed work, but copper dulls the shock back up your arm, doesn't damage the striking end of the pin punch, means you don't really need eye protection and leaves the hammers with nice clean shiny faces for hitting nails accurately.

It's around 10 quid for a Thor copper & hide mallet, it gets used for tapping down work in the machine vice on the mill and tightening the vice handle, the latter always with the copper face The current one has had maybe a decade of use so that's something around 1/4 of a pence per day.