While not parametric, this model is parameterizable.  It is set up to hold 4 ¾" lengths of PVC pipe while you paint them.  To use, print 2 holders and toe screw one to a 2x4 or similar piece of lumber. Load the lengths of PVC pipe to paint onto the fastened holder.  Fit the plugs of the second holder into the ends of the pipes and toe screw the second holder to the 2x4.

Make sure to not fit the second holder tightly so that you can turn each pipe to paint the sides and back.  You can leave the pipes to dry in the fixture between coats.