This necklace is from our new Monte Luna collection. Each necklace is made with lab grown diamonds and can either be ordered in 14 karat gold over sterling silver or in rhodium over sterling silver. Please use the drop-down menu to select. The necklace is approximately 3/8 of an inch in thickness. The necklace is 16 inches with a 2 inch extender on it. And can be worn at 16 inches, 16 1/2 inches, and 18 inches. Unfortunately, there is not an option to make this 20 inches but please inquire about an extender.