Rethreading screws (the search for replacement screws)

[Jimi]

I am in a pinch ...

I think I need to replace a shoulder screw. It all looked like the sunny side of the street, that it would be a regular M5 screw. A slotted screw, but still ... no problem. Off to the local store, bought a box.

At home I tried it, and well ... no luck. Remeasured, still looks like it should be M5.

Waffling around on the internet, I happened to see references to M5 having a finer pitch (0.75 mm) earlier on (pre-1970). Short of trying to build a time-machine and go back in time ... what are the options?

Can one rethread a standard M5 screw? Would a machinist be able to make a bunch of replacement screws from an original one?

EDIT:

I am adding a photo of the screw, this should be in the swing mechanism of a Sinar Norma. I measure it as 17 mm long, with a diameter of 5,19 mm.