I've designed a made to measure thumb screw adjuster now.. There are two printed parts to it that are quite small, so I'm trying to figure out a way to print them so I don't have to pay the minimum part cost price twice.. If I can do that it'll cost about £5 all in.
I'm waiting on the bolts to come through so I can get the measurements exact, then I'll lump it in with the order for the first batch of hooks.
(The attached photo is a rendering, not the real thing.. but the real thing will look very close to it once it's sprayed / dyed black )