Model D magneto cowl /fan cover screws

[noel]

Can Anybody out there tell me the thread size and pitch for the three countersunk screws that hold the fan cover in place. Its a 1956 150D.
They look like M4 with a finer thread.

[Rob Miller]

I’ve just tried a standard 4 mm screw into a NOS cowling and it went straight in. I would run a tap through to clean the threads up on yours. Someone has probably forced a BA screw in at some point.

[noel]

Thanks Rob
Thats quite possible. The screw that is in there is a finer thread than M4 and I found BSF bolts holding the number plate on. I thought it was worth checking before trying anything that might ruin it.