It looks like one of the bigger 29's (like a 29k71 or so)
Imagine a machine that can sew the tops of two cowboy boots together without straining at the thickness...
Imagine that you can leave the material in place and still stitch your name into it by rotating the foot feed mechanism
The ONLY reason I sold my 1906 29-4 is that I got the 1868 Politype Patcher...