This Double Tube Collar is made from Surgical Steel. Why not have a matching collar to go with all of your piercing Jewelry. We also have the matching bracelet too. It is very stylish and it comes in three different sizes to accommodate most all neck sizes. The thickness of the collar is approximately 1/4 of an inch. We measure these collars the same way that you measure for a Captive Bead Ring. We measure the inside diameter only it is not like a normal necklace. So you would want to hold a ruler to your neck and measure the largest part to get your necklace size. Also to check your measurement you can use a cloth tape measure or a string to measure your neck and then divide that measurement by 3.14 and that will give you the diameter if your neck where a perfect circle. Because the shape of your neck is not an absolute perfect circle this is just used as a way to check your measurements.