You'll find UNF fittings on the Bristol disc brakes. I would expect those bolts to be 7/16 20 tpi UNF. The smaller size, such as on the flexible hoses are 3/8 UNF 24 tpi.
They were Dunlop brakes, so the UNF thread would have come from Dunlop's use of it.
Those bolts that Geoff mentioned match the part numbers in the 406 spares book. They are probably similar to what was used on Jaguars such as the XK150 around the same time .
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