Blood knot tool
thingiverse
I printed the parts in PETG, but PLA should probably work, too. You'll need to bend some heavy gauge wires to make the pincer arms. I used Monkey Hook Picture Hanger Hooks from Home Depot. You also need either either latex tubing or silicone tape to wrap around the top arms. The picture shows a printed tool next to a purchased Dennison Blood Knot Tool. I have not added the silicone tape to secure the clips yet on the one I printed. Here is a YouTube video (not mine) that shows how to use the tool. https://www.youtube.com/watch?v=K9RMpiAcsy0
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