Well after an afternoon of rummaging through various boxes and cans of bolts I have found one a bit longer in 1/4 UNC, I have run a tap down the filter housing again 1/4 UNC (1/4 and 6 mm use taps always difficult to find, they break easily) and with a fibre washer all assembled and fitted!
Next question is, I intend to fill and run the tractor on white road diesel , for the amount I will use it’s not worth the effort to get red diesel.
Is there a down side to white as it is a higher cetane number?