I recently ordered some modestly larger screwless vises to get keyed and setup for the table on the Hurco. They all came with an extra pin. It looks to be about the same diameter as the cross pin on the bottom of the live jaw lockdown mechanism, except they are about twice as long. Maybe to be used in place of the shorter pin, but go through the side holes instead of just locking in the notches on the bottom for greater strength on special applications?
None of my other screwless vises came with such a thing. These are the biggest ones I have bought though. My next biggest ones are 5" wide by 6" jaw opening. These are 6" wide by 7" jaw opening.
(I plan to step cut the jaws for a slightly bigger working range for a special application without increasing the foot print of the vise by going with a bigger one or a lock down one.)