Just doing some more experiments, I have bought a set of taps for this spec but have found a UK or even European supplier of bolts or screws non existent.
I have some on order from China but this will take some weeks.
Anyone know where you can buy these?
People who sold me the tap said it was an odd size (after they sold me it) and went on to say Metric fine is unusual under M8.
Standard thread size is 0.5 for M3.
It is for fitting a scope ramp to an old air-rifle. Glue plus screws.