Parametric 1/2 inch Popup Sprinkler Riser

I have an older lawn and over time I have had to add extension risers to raise my popup sprinklers. Unfortunately the cheap store bought cutoff extension risers break with the slightest bump from the lawn mower wheels. Ok, so this design is not the most creative way to use a 3D printer, but it does make a darn tough part.
I precompiled the 1/2 inch pipe threaded parts, using DaveGadgeteer's threading library, into .stl files so you need to download the .scad and .stl files into the same dir