Injection blow molding could be an option, though it might be a specialized machine and pre-form to get that mixture of OD and wall thickness. Draft and undercuts aren’t usually problems because the parts get pushed off the machine with air.
We’re dealing with something similar now, but larger OD and much thinner wall (like .5mm). The plan is for injection molding but we aren’t to that stage yet.
Sorry maybe I should have explained a little more:
The design I have at the moment is for two rods (one solid , one a tube) with the solid sliding into the tube. So a telescopic arrangement, with bump stop at the end of the outer rod and a t-piece top of the solid rod, so the solid cant slide all the way out of one end of the outer rod.
So unfortunately likely can’t be bought in from pre existing plastic tubing.
Anyway I think I’ve found an example:
Looks like maybe its not the usual manufacturing approach, but it can be injection molded with long pins. On a side note I was told each pin adds around $800 to the tooling cost for steel molds.