Knob has long patented shank. Called 423 Design in 1888 Chicago catalog page 104 and 1895 catalog page 72.  Shown below are pictures of  Niles construction .  The knob has standard  NPT pipe threads. The threaded steel shank with a bronze sleeve is screwed into the knob. It is locked in place with a small steel pin. Click on pictures below to see larger image.