There is a single screw at the center with a very long 3 inch screw with a cover plate at back and a nut on the end of the long screw.  

The knob pulls are 1.5 inches across and 1 inch tall and are round and have a domed curved top.

CONDITION:  These were purchased for a project I never completed.  Two of the knob pulls are perfect with no issues.  One of these, upon close inspection has two very small chips or imperfections near where the screw would go into the center hole.  I never noticed this when purchased and was certainly a manufacturing issue. The imperfections are about 1/16" near center hole.   These are all usable and bright and attractive.

This listing is for the set of 3 knobs.