Flat bottom #238 O-Ring

A #238 o-ring measures roughly 3.50" on the inside, 3.75" on the outside and has an 1/8" cross section (actually closer to 0.139")

I had a water filter with a bad o-ring (squished flat over many years). I got a new o-ring which seemed to  grab and twist every time you tightened the top (even with grease - which led to leaking). Then I got one of those brainy ideas involving a 3d printer. I tried printing a round o-ring - that DID NOT WORK! Then, since the top of the filter is flat, I got the idea to print a flat bottom o-ring - it prints nicer too!

I printed in a 90-ish durometer TPU. One thing you do need to look for - set the slicer to print with random start positions and absolutely no infill - all walls. Layers lines should all be perfect nested circles. 

So far so good on my filter… I wasted way too much time on this - I could have bought piles of o-rings and just swapped them out every time I changed the filter. I could have bought many different materials of o-rings - silicone, nitrile, etc… but instead you get this lovely flat-bottom o-ring model. (enjoy!)