Inside Diameter of the bottom ring with lock : 1.47 inch/40 mm - 1.77 inch/45 mm - 1.97 inch/50 mm
The Thorns themselves have an inner diameter of about 24-25 mm
Internal width : 1.37 inch/35 mm
Anti Slip ring available: 1.3 inch/33 mm - 1.38 inch/35 mm - 1.57 inch/ 40 mm
Material: High Quality Medical Grade Stainless Steel 316 L, no chrome plating, no rust guaranteed.
To ensure proper fit, measure the width of your cock (take that measure at the base). Once you know your diameter, you can choose the size that will fit you the most, by its size and comfort.