A simple cord tensioner hook to be used for guylines, ridgelines or lines of any sort when camping or during other cordage-intensive activities. I use (and recommend) it in combination with my BEEFY TRI-LOBE TENT STAKE CAP for a killer tarp-staking setup:
https://www.prusaprinters.org/prints/35604-beefy-tri-lobe-tent-stake-cap

Fix it at one end by a larkshead knot through the eyelet at the bottom. Then hook the to-be-tensioned cord through the hook, pull it tight, and wrap it around the curved top back down and force it into the toothed slot. Done.

Print instructions

At 100% scale, it is ideal for 3 to 4 mm cords. For my use with 2 mm guyline cord I scaled it down to 75%.

Print with 100% infill lying flat.