Wulff, you got it right. I spent my entire career, (1961 - 2007), in manufacturing, from machine operator to toolmaker to project manager.

First of all 6061 T-6 is very expensive. In order to operate profitably there must be a minimum of waste. Labor is also very expensive. Anyone manufacturing reels in quantity would use CNC machining centers set up to machine round bar stock approximately 1/4" larger than finish diameters.

In theory, any size or shape that would finish at the required diameter could be used, but the cost of material and labor would be prohibitive, and, unless the stock was round, the grain structure would produce an inferior product.

In short, although it is possible to make a reel from any size or shape material, it would never happen in a production setting. Might work for a one - off prototype, but even that would be highly unlikely.