Please allow me to visit from over on the XK list.
Here is a picture of a home made screwdriver type tool for adjusting the fuel mixture screw on a SU H6 type carburetor.
The mixture screws are on the very bottoms of the carburetors, and cannot be easily seen in the narrow XK engine compartment, and while trying to adjust the screws on a running engine my normal screwdriver kept slipping off.
So I ended up making this little screwdriver having a cylindrical part which surrounds the screw head, allowing easy one-handed mixture adjustment without worrying about trying to hold a screwdriver upside down under each carburetor, without it slipping off the adjustment screw.
The tool was made by cutting and filing a flat piece of steel to shape, with a short piece of copper tubing soldered onto the screwdriver end.
The hex shaped portion can be used to first remove the protective cap, exposing the mixture screw.