John's specs are correct,but actual barrels can vary by a few "thousanths" and still fit.The .900 shoulder cited by John is correct for the military 88 with the tube.Since this is an octagonal barrel,it is civilian and would likely have a useable shoulder.The Haenel Mann. have similar threads and this barrel may have come from one of them.With care,this barrel can be used on several different actions.The small thread 98s and Swedes come to mind.
Mike