We have a glass door knob with 8 sides.  We only have the 1 of these.  It has a star/flower center and a brass metal lower portion.  It measures about 2 1/4" across the center front x about 2 1/4" in D.  The threaded portion on the bottom is round with the inside measuring about 3/8" across.  It is in nice conditiion with the brass being slightly tarnished .

Glass Door Knob 8 sided Vintage Item