To increase torque with a slotted screwdriver, which dimension must increase?

• A. Tip width
• B. Shank length
• C. Handle diameter
• D. Blade length

Answer: (C)

Torque from a screwdriver comes from the turning force you apply at a distance from the screw’s axis. When you grip the handle, the distance your force acts from the center of rotation is basically the handle radius. Increasing the handle diameter makes you apply force farther from the axis, enlarging the lever arm and thus the torque you can generate with the same grip force. The other dimensions don’t increase that lever arm: tip width affects how well the blade fits the screw and how effectively torque is transmitted, but not the leverage; shank length changes reach and rigidity without changing the lever arm; blade length affects engagement depth but not rotational leverage. So, the dimension that increases torque is the handle diameter.