Reluctant to even suggest this, but maybe it's left-hand threaded? Sorry if it's obvious and you've tried already.
Haven’t tried that. But it had fold up tabs to stop it rotating, being reverse threaded as well seems a little much for something that’s only there to retain something. Doesn’t make sense for it to be reverse thread.
@Nef started
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Reluctant to even suggest this, but maybe it's left-hand threaded? Sorry if it's obvious and you've tried already.