I need some 10mm long countersunk machine screws for Pegler Belmont
lockshield radiator valve caps but can't work out the size and Pegler have
ignored my requests. M4 is too thin and M5 too thick. Can't find any to
match up in the shops. Anyone know which imperial size comes between the
two? Would it be 3/16" (nearest equivalent to 4.5mm)? I'm not sure how
imperial screws are measured.