Our Pro-4 Grooved Axle starts life as an official B.S.A. Pinewood Derby axle. It is C.N.C. machined true and round, we then add 4 grooves (1 behind the axle head and 3 in the hub contact area) to reduce friction and hold graphite then head is back-cut for further friction reduction at the hub face on the wheel. They are semi-polished so the builder can finish it their spec. The Pro-4 Grooved Axle is our preferred choice when using a Racing Graphite Lubricant.