Thanks to all who responded.

After seeing Dave Billington searching on "19 TPI" I did the same and found
a reference to it as an obsolete thread called "Copper pipe thread".

Thanks again

Paul K. Dickman

See below;

1.. Thread "Pas des becs" by Robert GIRARD )
Posted: Nov. 11, 2002 @ 14:22.
Hello I repair lamps in Provence, Luberon, France !!!! Could someone help
me to find the origin of threadings used in lamps, called in France "pas
français" : "Pas des Becs", or "Pas des becs de cuivre" = 10,85 mm diameter
and 1,33mm thread (19 thread/inch) ??? - and the others : "Pas de Paris"
(16,85mm diam.) and "Pas de Rouen" (!!!???!!!) ????? and the threads (may be
Withworth ? Empire ? or other ?) used to screwed ancient statuettes on their
marble base Thanks Best rgds RG

1.. On Nov. 11, 2002 @ 17:47, Alex Marrack ) wrote:
Thread names are often confusing, the first one you mention is the one
often used on French Gas burners and earlier French electric lamps. It is a
whitworth form thread, and is a 'non standard' size of English Pipe thread,
now standardised as British Standard Pipe thread, but dating back to about
1820 and maybe before.
The 19 TPI persists and is still used for 1/4" and 3/8" pies now (these
threads are bigger than the name implies and the 1/4 inch size pipe has an
OD of nearly half an inch (Dont ask!) The odd size thread was used over here
(UK) and called Copper pipe thread, not widely used for over 100 year.