Drill America Cobalt Aircraft Extension Drills 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 typically used to identify cobalt steel tools; performance is similar to uncoated tools. Drill America Aircraft Extension Drills are manufactured to National Aerospace Standard 907. The 135 split point is self-centering and reduces thrust. Sizes smaller than 1/16 in. have the 118 standard point. Drill America Aircraft Extension Drills are available in 6 in. and 12 in. overall lengths when extra reach is required.