I went back and counted 7 blades per gang. If you go with blades that are 1 MM thicker than what is on there, you will use up about a extra 1/4 inch of your threads on the axle. No big deal. Ken Sweet
ok went with 20" 4.5mm, they fit and man are they big, I have enough thread for a slotted nut, have to drill the holes and install the cotter pins, almost finished with the refurb. thanks for the help.