The Promat is completely Metric through and through but the 8mm shafts convert to .315" which is very close to 5/16" (.3125). The Emmons PP swivels will fit the Promat bell cranks and the Emmons bell cranks fit on the Promat shafts (as long as the nickel plating isn't too thick on one or both, to cause interference). I found that the plating on most of the Promat parts is fairly thin. There should not be any problem using a Promat bell crank on a 5/16" Emmons shaft.
It would be interesting to see how much Mr. Papic charges for his bell cranks. Emmons PP bell cranks are getting increasingly harder and harder to acquire.
Here you can see another Promat parts. Thanks for info Lynn. Yes, dimension 8,00mm (to tolerate 7.94mm) ... For more info or another dimensions you can contact directly to: www.promat-steel-guitars.com
PROMAT PRO S10, PROMAT SE10 Economy, Goodrich, Fender Steel King.