[A Snake]

Coyled,

Billet just means that they are machined out of a solid piece and not cast. Normally, such things are machined first, then heat treated. Final machining (grinding) brings the piece into tolerance after the distortion of heat treating.

It may be hard to spot after having the broken parts rubbing eachother, but look for (or have a machinist do it) crystallization. This could indicate either excess hardness when made or, enough heat was generated from stress to make the metal brittle.

Do you see any colors on the metal near the break that are different from the rest of the hub? You're looking for colors ranging from a light straw color to a dark blue. These are heat indicators and may tell us more of the story.

Al