The tunnel you see in the picture is made of surgical steel. The thickness of the metal is incredibly thin, so it may appear smaller than it actually is. The thickness is approximately 0.02" (0.5 mm). The tunnel is teardrop-shaped, or pear-shaped if you like. You could almost say the drop is a bit chubby. 

The jewelry is available in 9 different sizes, the smallest being 1/4" (6 mm) and the largest 1" (25 mm). Under normal circumstances, the diameter of a tunnel is measured by simply measuring the outer edge. But since this tunnel is teardrop-shaped, this can't be done. Therefore, you measure the edge around the tunnel. This can be done by taking a string around the tunnel, then measuring the length of the string, and then converting it to the diameter. But don't worry, because we've done the work for you. If you have a stretched earlobe of 1/2" (12 mm), simply select the diameter of 1/2" (12 mm).