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I thought that but I didn't think 13x1 was a standard or common thread and 14x1 was more likely, but as you say its pretty undersized

Tried that at mitre 10 today but their selection is limited. Blacks might be the way to go.

I have taken possession of a sako 75, looking at getting a suppressor for it but I'm not sure about the current thread. It's close to 1/2x20 but a little too big.
Diameter of the thread is 12.9mm....