Please note I have printed but not tested this design, so consider it a work in progress. I was surprised to see that no one had drawn these up yet, so I went ahead and gave it a whirl. Better than paying over $1 each and having to wait for delivery, right? UPDATE: After testing this out, it needs some work, particularly to the locking ring. I'm thinking a smaller diameter and thicker locking tabs. Will rework it and post it back up as soon as I get a chance.