Drill America Cobalt Aircraft Extension Bits are similar to high speed steel, but with more cobalt for improved performance when cutting harder metals such as stainless steel or nickel alloys. Gold Oxide is a thinner oxide surface treatment than black oxide normally used to identify cobalt steel tools. Performance is similar to uncoated tools. Drill America aircraft extension drill bits are manufactured to the National Aerospace Standard 907. The 135° split point is self-centring and reduces thrust. Sizes smaller than 1/16 inch. 118° standard tip Drill America aircraft extension drill bits are available in 6 inches. and 12 inches total lengths when additional reach is required.