There are many designs like that, the one I picked for source is just the most pretty I used, it's not that it was of particular value in terms of inspiration. Problem is all these designs are either wrong size or ugly and never customizable so I thought I'd solve that problem once for myself (and share here while I'm at it).

The dimensions of supplied stl is for all e3d couplings I have around, if you have different hardware, feel free to customize.

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