@Lambie The OED (2nd edition) defines fastener as "2. That which serves to fasten anything.".

I think it's absurd to say that something can be said to fasten, but at the same time cannot be called a fastener. I agree that the notion of a screw might not be the immediate association to the word fastener (or even fasten, in my opinion), however, but that's beside the point.

@Man_From_India But the time the situation occurs is a very definite time, even if we don't know or care what it is.

@userr2684291 Yes, that which serves to fasten. There's a physical difference between nuts, screws and nails which makes them different from fasteners. They are all single shaft, threaded or not. It would seem that few here have any personal experience with this at all and are quoting their finds. One BrE said the same thing I did. My suggestion: go ask a builder.....a mechanical engineer may classify screws, nuts and bolts under fasteners, but a builder or carpenter would not.

Cunningly difficult question!!!!:

@snailboat Wow, snails have tongues! Who knew???? (apart from you)

@CowperKettle I reckon it's probably anti-PF1 monoclonal antibody. The reason is that monoclonal antibody occurs over 4, 000 times in the BYU i-web corpus, suggesting it's a compound noun to me. So then Anti-PF1 would be a modifier of that compound. Just a thought. Maybe check with @snailboat for second thoughts on that ...

And take into account that that's just armchair theorising ...

@CowperKettle @snailboat OK so checking on i-web with [* monoclonal antibody] and [monoclonal * antibody] they both seem to exist with lots of anti-XYZ thingies in both positions. So my guess is that nobody knows! :-)