This is a very hard to find solid brass Thomson-Houston socket. Sockets like these were last used in the early 1900's. In 1900 they had a remaining market share of just 10%. Due to the invention of Edison base adapters for these sockets, and an agressive campaign to market them, by 1905 these sockets had disappeared completely.
Below is a bit of info about early lightbulb sockets taken from the 1927 book, 'The History Of The Incandescent Lamp' by J.W. Howell and Henry Schroeder:
Soon after the commercial introduction of Edison's lamp, many other concerns began making lamps, each with an individual design of base. This required a corresponding socket to fit the base and no less than fourteen different designs were in use at one time or another.
In 1900, the more important designs in use were the Edison, which covered about 70 per cent of the total, the Westinghouse, 15 per cent and the Thomson-Houston 10, per cent. The remaining 5 per cent covered the other designs.
Standardizing the Edison Base
As the use of incandescent lamps became more general and the necessity arose for more types of lamps to meet individual specific requirements, together with the need of stocks at convenient distributing points throughout the country to supply the demand promptly, the existence of so many different lamp bases presented a situation which, if continued, would seriously retard the development of the electric lighting industry. The necessity for overcoming this condition seemed imperative and it was recognized that something must be done to simplify the lamp base problems.
The task seemed insurmountable. At this time, 1900, there was an aggregate of about fifty million sockets of various designs in use in the United States. It seemed desirable to standardize on the Edison base and socket because of the simplicity of its design and extent of its use. To change the sockets of the types other than Thomson-Houston and Westinghouse to the Edison type of socket was considered possible, but to replace every Thomson-Houston and Westinghouse socket with an Edison screw socket was thought impossible. It appeared, however, that adapters could be designed to enable existing Thomson-Houston and Westinghouse sockets to receive lamps fitted with the Edison screw base, but even this was considered by many to be impossible of accomplishment commercially. Nevertheless, believing that it should at least be tried, the adapters were designed and made, being sold at cost.
The campaign, which was started to effect the corresponding changes commercially, was so successful that in less than five years the demand for lamps in the United States with other than the Edison base practically ceased. At the present time, the five hundred million sockets now in use in this country on commercial lighting circuits are all of the Edison screw type.