According to the relevant
Lucas Workshop Instructions, the gap should be between 6.5 and 7.5 mm
(0.256" and 295" - 1/4" and 19/64") from the tip of the screw to the slip ring.
We favour the higher value, especially if the engine has a high compression
ratio, so as to avoid any unnecessary jumping to the safety screw.
If you shorten the screw so as to achieve a larger gap, the tip of the screw
should be rounded.
Do not enlarge the safety screw gap above the higher recommended value,
otherwise you may encounter the problems discussed under our FAQ
What do safety screws do?