*Warning: there are many grades and series of steel, but few are ideal for internal wear. Only 300 series surgical steel is recommended for body piercing. The highest grade of 300 series is 316L, which is the grade used for surgical implantation.  316L is THE ONLY grade that "binds" the nickel in the steel, which guarantees no nickel will leach out to contact with the wearer. 

Many people develop allergies to the nickel as a result of wearing cheaper grades of steel. Nitrous recommends only wearing 316L Surgical Stainless Steel.