Piston Ring Set 73mm.  72mm + 1.0mm (+40 Thou). for the 300cc Engine.  These rings maybe new old stock that have stored for many years they have been opened to check condition and found to be as new. Look to get about 4 thou per inch of the cylinder bore end gap in your rings as you would normally when you fit piston rings, if you don’t know what I am talking about seek help. New supplies may not be Hepolite as shown in the picture