Containing 13 500-12 long series aircraft extension drill bits conforming to NAS907 type J, in fractional sizes from 1/16” to 1/4” in 1/64 “ increments (13 drills in all), the CO500-12 set represents great value. The drills in the set are manufactured from premium High Speed cobalt so are suitable for drilling in many materials, including steels, stainless steel and aluminum and have a long overall length of 12 inches with short flute length to provide stable drilling in hard to reach areas. The drills have a 135 degree split point, designed to self-center, with low thrust for better penetration, and a bronze oxide finish to prevent workpiece material from sticking to the cutting edges of the tool for cleaner, more accurate holes.