Many thanks for that tip I Will bear in mind for the futureIf you cut a slot in the bolt at right angles to the threads (just on one side) with a bit of WD40 or diesel, you can clean the threads, if needed.
It would appear that metric thread's are very similar to unf
A 6 mm bolt fitted nicely so with plenty of heat and quenching with Cold water it came out easily
The problem I have now is getting the quadrant out I have got it to move out about 5mm
Now it won't come out any further although I can turn it quite easily