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Old 3rd Sep 2019, 11:22 pm   #12
emeritus
Dekatron
 
Join Date: Jan 2012
Location: Brentwood, Essex, UK.
Posts: 5,316
Default Re: Unknown Edison Screw Lamp Holder

A useful feature of the French lampholders I have seen is the provision of a small grub screw that positively locks the lampholder to the (usually 10mm) thread of the fitting. It ensures that you unscrew the lamp from the lampholder rather than the lampholder from the fitting. Before adopting the 10 x 1.0 mm thread, the older French standard thread for lampholders was what is now referred to as 11mm thread (but is actually 7/16" BSF), for which brass adaptors were readily available both ways to 10mm when I last visited France some 5 years ago.
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