Thanks to the two replying members, will have a measure up and follow your advice, I take that from the lack of replies that not many people have these machines or , really don't know themselves, thanks again you two, appreciated.
Somebody knows... Maybe you?
I just went and checked in the ball container that I throw any spare balls into. And I found a bag full of used plastic balls that I'm sure came from a hockey machine, could be some dating back to the R&W I did, though probably a Seeburg I restored too! There is one very old red plastic of some kind that I'm sure was from the Seeburg, sized16.84mm (21/32") And a bunch in old but newer white plastic sized 17.55mm ( 11/16"). I imagine the reason I have so many spare is I replaced them in the Seeburg machine. Should be very close to the R&W machines I think.