This is an antique knot pin dating to 1900 made of a sheet that has been rolled into a tube and plated with 10 karat yellow gold.  Ornate engraving decorates the sides and center of the coiled "knot" which ends in a finely coiled tendril at the center and is believed to represent a horse crop or whip.  Pins like this were popular during the Edwardian Period when the sport of horseracing was made popular by King Edward.  Weighing 6 grams and measuring 1 1/4" wide by 1 1/8" tall, this pin is 10 karat heavy gold plate.  Due to some wear on the front of the pin, it has been replated.  The back of the piece has a "C" hook closure, a tube hinge and there is an additional hook that could have been used to add a chatelaine to the pin.  The extra hook could be used to add a chain to form a pendant.

View of the back: