clamp screw size for M2 hot end

[parshall]

Hi,
i recently inherited an M2, and noticed that it's missing the clamp screw for the hot end. I don't know how it's managed to work so well without one, but now the hot end won't stay in place when the extruder pushes filament.
Anyone know the clamp screw size?
thanks,
ep

[airscapes]

Can't take it out right now but looks like an M3 at least 8-10mm long