Hi Mark, the ignition module (coil pack) bolts are M6 x 45. (so M6 tap, usually 1mm for each thread).

Probably worth buying a tap & die set.
The bolts should only be tightened to 10 Nm / 7.38 ft lb
If you require new bolts:
Part # 11518067 - Screw,HEX.HD.,M6 X 45,Ignition Cassette to Cylinder Head Cover