Was that a rented mule or a pet?
All of the fitings ( end caps and threaded female adaptors) that will
fit shcedule 40 ( or 80 } PVC will fit aluminum pipe. Schedule 10
aluminum pipe is good if you your mule is not to clumsy. The PVC
fitting work good if you rough up hte pipe and use epoxy. IF your
mule is really big schedule 40 is the same OD, as in schedule 80 in
situation where you are backpacking with an elephant.