I have made plenty of dumb stock purchases, but some 1 foot-long 15 mm
diameter aluminum rods are being very useful!

By chance, they fit my 3D printer spool holder perfectly, with bearings on
hand, to hold filament spools. Just had to make plastic spacers for spacing
between the bearings and the spool.

Can't believe it fit the 3D printer rod holder, perfectly. Didn't even have to
cut the rod... lol.

One might also be useful for driving a bicycle chain.

Gonna find out if plastic spacers will hold a bicycle sprocket...

I would like to use metal, but it's very difficult unless you have a metal
lathe or maybe one of the new cutters. Cutting practically anything in
aluminum with decent precision has been difficult.

Might try one of the new light duty aluminum cutters, but obviously it will be
a lot messier than a 3D printer. But at least it (hopefully) won't spray
aluminum chips all over the place like a miter saw does.