Planning to use a short piece (2 or 3 inches) of 5/8" outer diameter
aluminum tubing. The wall thickness will be 1/16" to 1/8".

Pressing down on the center of the tube will be a maximum momentary
pressure of very roughly 300 pounds (a wild guess).

Is there any difference between 6061 aluminum and aircraft grade
aluminum for that purpose?

General ideas about the differences between the two would also be
appreciated.

Thanks.





FWIW:
With the aluminum tube end inner surface roughened, if I can get the
inner diameter correct so that the aluminum tube end can be glued
snugly around the motor gear, that should be straight and hold very
well. The aluminum tube might also provide good heat sinking when
spinning fast.