The number on the wrench isn't in my book, so it's probably towards the latter end of the date range , also the T prefix puts it after 1913 or so at least (I don't have good data on when the prefix started). I would think possibly as far as 40's myself, but not much later than that as it looks to be a carbon steel wrench.
>I wonder if it was used on airbrakes on trains?
Given it's size and pattern, I would guess it's a compressor head or cylinder wrench. (The compressor supplied the air for the brake system, so there was one in each locomotive). Westinghouse however also sold the air compressors to others as general purpose machines and supplied a set of wrenches with them.
(However, I suspect far more were sold to railroads than industry...)
