Summary A unique linear bearing with spring-loaded arms for leveling and cushioning. The test slider in the photos was designed to run on 1 1/2 inch fence pipe or conduit(?). There is also an .stl uploaded is for 1/2 inch PVC pipe - I thought that might be useful to a broader audience. How I Designed This Pipe size comes from my PVC pipe library. If you want other sizes that might be a good place to start. ;) http://www.thingiverse.com/thing:222574