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I was thinking that the aluminium compression cap, once torqued, acts like a sprung washer. Preventing it from coming loose. While the steel is too stiff to load-up like that
If there's a difference, I suspect it has more to do with coefficient of friction than spring modulus. Aluminium is very grippy compared with steel. Anyway, buy one on my top caps and use as directed, problem solved 🙂
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