Premium-grade silicone. Due to the nature of silicone these are flexible so not as secure as harder materials Silicone cage - Cage Length: Approx. 65 mm, Cage Inner Diameter: 32 mm. Extremely comfortable to wear 24/7 4 x Spacers, 4 x Different Length Locking Pins. Perfect for fine adjustments for a great fit 5 x Rings Approx. ( 40mm, 42mm, 45mm, 48mm and 50mm). You can get the right ring size from the selection provided Use with a plastic padlock and you can even go through airport security wearing this device. We include a free Brass Lock With 2 Keys.