Just Googled brake adjuster and there appears to be at least 2 sizes that are common - M7 and M10. I would think the M7 (or potentially even an M6 if you can get one) would be the correct size.Assuming I am understanding your problem correctly you might be able to use a bicycle brake adjuster like this. I used one as it allowed me to adjust the tension after replacing the cable. I think I had to slightly enlarge the hole in the metal housing. Should be easy to source from a bike shop or an old bike in the garage perhaps??
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