This style of porcelain knob has the imbedded back screw. It is an old knob and, therefore, has an old patina with some crazing here and there.
The knob measures one inch across the top. The base is 3/4 inch across. The knob projects 3/4 inch from the surface of the drawer or door. The imbedded screw is 5/8 inch long.
Porcelain knobs like this were used on a variety of furniture pieces and cabinets. Since porcelain knob have been around forever, it is hard to guess their age. We think this one dates to the early 1900s.