Most rear hubs use 10 or 11 1/4" balls; the Helicomatic used 13 5/32" balls. The smaller balls were needed to move the drive side bearing outboard, like modern cassette hubs, because the Helicomatic freewheel takes up more room than a freehub. The problem with using smaller balls is that they wear more quickly, and often were not maintained as frequently as they ought to have been. While the balls are not hard to find, cones ground for 5/32" balls are a different matter. If your cones are still in good shape, and the freewheel still works, repack and enjoy, but remember frequent maintenance to keep it running!