Threads are standard metric coarse (most common).
M3 x 0.5mm pitch; 1.5mm allen key.
M4 x 0.7mm pitch; 2mm allen key.
M5 x 0.8mm pitch; 2.5mm allen key.
M6 x 1.0mm pitch; 3mm allen key.
M8 x 1.25mm pitch; 4mm allen key.
M10 x 1.5mm pitch; 5mm allen key.
Screw lengths are measured overall, to the point tip.