I think they are 3mm on the thread and 8mm length as I see from the Screw**x site you are supposed to count the head. Do you count the head in the thread width as well?
Oh @wild edges so far out of my comfort zone, what makes them M4 and not M3 please?
"The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it." Sir Terry Pratchett
The M bit is the thread diameter in mm. They generally taper a bit at the end so try measuring in the middle. You can see the taper in the pic below. Yours look like 3mm at the narrowest point so will be 4mm by the middle.
If you can keep your head, while those around you are losing theirs, you may not have grasped the seriousness of the situation.
The M4 4mm countersunk screws just arrived and they are a perfect fit! So many many thanks @wild edges I now have two usable bird feeders (once they are washed) and less fear about dropping the little screws in the future
"The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it." Sir Terry Pratchett
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Oh @wild edges so far out of my comfort zone, what makes them M4 and not M3 please?