The most common names for these watches were “Thin-Thin,” “Thinline”, or simply "27 Jewel” and “30 Jewel”. In my opinion, the most accurate name is probably the one written the watch dial itself: Elgin “27 Jewel Self Winding” and Lord Elgin “30 Jewel Self Winding”.

The lack of clarity around the correct name has unfortunately led to stories that have no basis in fact:

“Thinline” was actually the third name used to market these watches, not the first:

There is also no evidence that Elgin stopped using the name “Thinline” due to pressure from Hamilton using the same name for its watches. The U.S. Patent and Trademark Office’s database shows that Hamilton never had a trademark on “Thinline.” In addition, “Thinline” was occasionally used to advertise Elgin’s watches as late as June 1962 — almost the entire time these watches were being produced.

What is true is that Elgin did not use the name “Thinline” very much after 1959-60. The reason was probably to avoid confusion among its retailers and customers, and maybe as a courtesy to Hamilton, which at the time was both a rival (in selling high-end watches) and a partner (in trying to persuade the U.S. government to give the industry tariff relief). Hamilton had used “Thinline” in 1958, but then stopped using it in 1959, the year Elgin launched these watches. When Hamilton started using “Thinline” again in 1960, Elgin largely — but not entirely — stopped using that name.

During this time, “Thinline” was also the name of a widely-advertised line of General Electric air conditioners. Elgin may also have concluded that this name did not have a great connotation for a line of luxury watches.