FAA AMT (Aviation Maintenance Technician) Airframe Practice Exam

The included angle of a twist drill for hard metal should be 118°. This is because the included angle refers to the angle between the two drilling edges of the twist drill. For hard metal, a smaller angle is needed to provide a sharper point and better cutting action. Option A (90°) is too small and would not be effective in drilling through hard metal. Option C (135°) and D (160°) are both larger angles and would result in a duller cutting edge, making it more difficult to drill through hard metal. Therefore, the best choice is option B (118°) which provides a balance between sharpness and durability for drilling through hard metal.