In a batch of old tools I acquired I found a mere flat piece of metal,
steel I guess, very nearly rectangular, thick enough not to be able to
bend with my fingers, about 2 inches by 3 inches, not real shiny
anymore, and stamped into it is
Henry Disston & Sons
Googling Disston "No. 20" found me a lot of tool entries,
but no No. 20 for Disston. Usually some other number and maybe
another company like Miller Falls No. 20 Right Angle Triangle Level.