The Union Manufacturing Company came into existence at around the close of the Civil War. Made up largely of the Board of Directors of Stanley, the ownership and stock holders started the new company just down the street from The Stanley Works in New Britain, CT
In June 1904, John Carlton and George Trask, Union employees, were granted a patent for a blade adjusting system that employed two round brass knobs mounted on a threaded vertical shaft that, when screwed up or down the shaft, would increase/decrease blade exposure below the plane's bottom. (Basic depth adjusting)
The planes were given the moniker, X No. #. They came in sizes X-0 (Stanley No 1 equivalent) through X-8 including a fractional X-4a (4 1/2) and X-5a (5 1/2). There was no X-1 produced as is currently believed. The X planes also came configured as a series of transitional planes.
Attractive in design and precise in adjustment, the X planes were produced and marketed until roughly 1920 when Stanley merged with Union and the X planes discontinued.
I have used X planes of different sizes over the years and have found them to be high quality as built for that period. The larger sizes that I've experienced, X3, X4 X5, all performed quite well, with precise adjusting capability. The X0 not so much.
I found the iron on this particular example very difficult to sharpen, perhaps a poor temper, which caused it to chip during the sharpening process.
I also found depth adjusting to be difficult, mostly due to the small size of the adjusting knobs and the fine movement of the blade. There is no lateral adjusting mechanism and side to side movement is limited to the "slop" between the edges of the iron assembly and the frog sides. I'm not sure that this size was ever truly intended for heavy shop use.
Great looking example of an extremely rare plane, perhaps one of the few left in existence. Porter and Sons is the new owner of the Union Manufacturing trademark.