This pair does not look brass. They appear to have a nickel coating on the surface. They are old and have been scuffed. Each knob is heavy brass and came off of a set of horse hames.
Each knob measures 2 inches round and has a 3/8-inch long neck. The neck opening is 9/16 inch. There are two holes in the neck for nails or screws to fasten to the object.