Hmm, this is an odd find achim. Does the hole go through the full length of the handle into the place where the handle attaches to the head? I so... I wonder if Gillette was experimenting with TTO or two piece designs that early on.
If it's anything like the open-ended British NEWs, then yes, the hole goes all the way through. The threaded hole in the neck of the regular ball-end handles goes all the way through into the hollow-tube handle already.