I saw that Larry answered your question with "3mm by whatever." The "whatever" is 0.5mm pitch. The fasteners on bikes seem to have a standard relationship between diameter and pitch. 3mm bolts are 0.5mm pitch; 4mm bolts are 0.7mm pitch; 5mm bolts are 0.8mm pitch; 6mm bolts are 1.0mm pitch. Of course, there are exceptions! In any case, I think that this series of diameter/pitch pairings is sort of a standard and that sometimes a fastener will just be identified as M3, M4, M5, or M6. These designations seem to imply the pitches specified above. I also believe that some of the common thread pitches on bikes fall outside the metric standard. M10 is 10mm by 1.5mm (or is it 1.25mm?), but the 10mm parts on bikes (axles, derailleur hangers) are 1.0mm pitch.
I'll refrain from going on about Campy's strange mixing of metric and inch specs, such as 10mm x 26 tpi axles!?!?!?
Tom
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