Ok- who is the best thread detective out there?
A friend of mine sent me this picture and asked me to identify the thread.
It could be imperial, could be metric.
Almost impossible to say from the pic as diameter would also be handy. Looks like 1mm pitch and could be about 6mm Dia so possibly M6 but it does look course in the pic so who knows.
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Quite possibly 1/4" UNF as that is very close to 6x1 (had to sort a few of those Gorilla'd in to 1/4" holes in my time) OR it could be 5/16" UNF but the pitch is not coarse enough. Some good reference tables here: https://mdmetric.com/tech/thddat9.htm
As Robin said, diameter is the critical dimension.
Country of origin would probably help, for example USA or Canada then probably UNF, most other countries then metric.
Of course actually measuring the diameter would be the best help