21 May
2011
21 May
'11
9:31 p.m.
Alas they are not standard M3. After measuring up some
of the exisitng
screws, they appear to be 3mm in diamter, 0.6mm pitch (standard M3 is
0,5mm pitch). A look in a 1943 Machinery's Handbook suggests this is a
French metric thread.
Maybe wrong side of the pond but: Is it possible that they are 5-40 thread? (3.1mm major
diameter, 0.635mm pitch).
5-40 is still common today on barrier strips and I know was even more common on US phone
and telecom equipment from 60, 70 years ago.
I would not be surprised if barrier strip screw sizes had crossed the pond 70 years ago.
Reminds me of the Russian hi-tech chilled water cooling unit we had delivered in the
80's, we thought from the drawing it had some funky metric thread and we called around
to all the US metric specialty houses without luck, before we figured out that it was just
standard garden hose thread :-) !
Tim.