AIRCRAFT DRILL BITS 1/4 X 12in. FLUTE LENGTH 2-3/4in. - AIRCRAFT DRILL BITS. AIRCRAFT EXTENSION DRILLS ARE SURFACE TREATED HIGH SPEED STEEL WITH 135 DEGREE QUICK-CUT POINTS THAT WILL NOT WALK OR WANDER. DESIGNED FOR DRILLING THROUGH MATERIALS LESS THAN 4in. THICK. EXTENSION DRILLS ARE USED IN AREAS WHERE EXTRA REACH IS ANT.