Barrel parts
The barrel sub assembly parts.
Axle is 1/2" PVC pipe with a NPT pipe thread coupler glued on one end.
Axle nut is a 1/2 to 3/4" NPT adapter
A misc plastic "spacer" used to fill the gap when the pipe adapter is screwed on. Being NPT, they will only screw together so far before friction binds. It was not enough to clamp the tub tight.