The actual mount plate on the upright has four holes, one in each corner.

The press is bolted to it's mount plate with tapered head machine screws. The heads sit flush with the bottom of the mount plate, and so do not interfere with the seating on the press stand.

Showing the underside of the press mount-plate. Tapered machine screws hold the press to the press mount-plate. The four bolts are for the bolts to fix the mount-plate to the press stand.

Showing a mount plate with it's Challenger press attatched. The four bolt holes match the holes in the press stand. This allows the same press stand to fit either press.