This axle starts life as an official B.S.A. Pinewood Derby axle. It is C.N.C. machined true and round, Derby Worx then adds 2 grooves (1 large main groove and 1 small groove behind the axle head) 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.
Derby Dust is not a fan of original BSA grooved axles. Some racers swear by them. We just feel that they are so-so. The machining process is just not very precise. Has nothing to do with the company machining them. It has to do with the product your are starting with. If you prefer a grooved Axle, please take a look at VIPER or Titan axles as well. These are machined from a billet wire rod. Much better product that a stamped BSA axle that has to go through a machining process which can leave undesired end results.
Pinewood Derby Grooved Speed Axle utilizes grooves to serve as lubrication reservoirs and to reduce wheel to axle contact.