Hey KKj,

Your on the right track. The screws will be Nominal Metric size. 2.85mm is probably the right size for M3. a.15mm difference is only .005"/inch. 3.4mm is about the nominal size for M3.5

It's just a matter of determining the pitch? MECHANIC stated in his post that the O.S. screws were not interchangeable, so it leads me to believe they are a fine pitch thread.

Can you compare the thread of the M3 screw to a 4-40 bolt? Put one on top of the other and hold it up to a light. If it looks like the M3 has twice as many threads on it, chances are it will be a M3 x .35mm (fine pitch).
I calculated that the .35mm pitch works out to about 72 TPI (threads per inch). Almost twice that as a 4-40 (40 TPI). These will be bolts that may not be available at any corner store, mind you, your in Europe and it's a metric world over there. Good Luck.

Happy Fly'n....