Our Surgical Steel Circular Barbells are all 316LVM, this is NOT the cheaper commercial grade of 316L Surgical Steel that you are usually offered in Body Jewelry by other company's. Our Circular Barbell's are also threaded for a precision fit, made from 316LVM Surgical Steel, and the 8 gauge and larger, are all internally threaded, and smaller than 8 gauge is externally threaded. Circular barbells are designed for clients who frequently remove or change their jewelry. These barbells can be worn with virtually any piercing. Circular Barbell's are measured using the inside diameter.