This knob is the small size of the pre-1900 Eastlake knobs. It would possibly have been used on a small hanky drawer. It measures 3/4-inch across and has the typical brass cap found on these black painted wood knobs.
The threaded embedded bolt extends 1 1/2 inches beyond the back of the knob. The knob projects one inch from the surface. An old square nut is included.
This one is in excellent condition.