rrh wrote:
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.

Here is a selection from my table of common machine screw sizes, in
diameter order:

Type Size Diam " TPI Dia mm Pitch mm
BSW 5/32 0.15625 32 3.97 0.79
MF 4 0.157 50.80 4 0.5
M 4 0.157 36.29 4 0.7
BA 3 0.1614 34.84 4.10 0.73
M 4.5 0.177 33.87 4.5 0.75
BA 2 0.185 31.35 4.70 0.81
BSF 3/16 0.1875 32 4.76 0.79
BSW 3/16 0.1875 24 4.76 1.06
MF 5 0.197 50.80 5 0.5
M 5 0.197 31.75 5 0.8
BA 1 0.2067 28.25 5.25 0.90
BSW 7/32 0.21875 24 5.56 1.06

BA British Association
BSF British Standard Fine
BSW British Standard Whitworth
M Metric Coarse
MF Metric Fine
UNC Unified Coarse
UNEF Unified Extra Fine
UNF Unified Fine

TPI Threads Per Inch