156) The cutting speed for drilling aluminum, brass and bronze with carbon steel drills is______ Cutting speed for drilling mild steel with high speed steel drills.

157) The cutting speed of a drill depends upon the

158) In drilling softer materials, the cutting speed is ______ As compared to harder materials.

159) High speed steel drills can be operated at about ______ the speed of high carbon steel drills

160) The tap used to cut threads in a blind hole is