I believe there is a retainer ring that should go there like the one that is likely to be found in the tripod socket of your camera - it makes the hole smaller so it fits onto the standard tripod screw. I hope it's caller a retainer... I may be totally off though - I'm not the best with names and stuff
Also, Make sure that your Rolleiflex is the 80mm one to use with the pano-head, I found that the 80mm one lines up a lot more exactly than the 75 (I believe it's because of the difference in the nodal point - now that term I remember for sure! )