All stainless steels have “work” (or strain) hardening characteristics. It is particularly notable in the 300 series. When the drill bits contact the surface of the stainless steel and as they penetrate, the material will harden and it will be more and more difficult to continue drilling with the same pressure and speed. Drilling bits are generally made from high speed steels and monolithic carbide. It is important to lubricate the drill under pressure. Soluble oils or cutting oils are often used (it is advisable to seek professional recommendations on specific oils that are available for use with stainless steel). For long products and thick sheets and plates, the point angle should be 120 to 135 degrees. For thin sheets, in order to reduce the surface stresses, the point angle should be increased to 140 degrees and the relief angle reduced to 5 degrees*