PVC rod tubes
There are several types of PVC tubing/pipe. It is designated by a schedule #, (i.e. sched 20, sched 40, etc.,.). The higher the # the thicker the pipe wall and heavier the pipe. The O.D of all is the same thus the ID of the pipe decreases as the schedule # increase. I believe most rod tube are made of Schedule 20 material.Usually it is the heavier stuff (sched 80) that is not readily available except at plumbing supply house.