Double Twist Screwdr / Screwdriver

When tightening the screw by the use of screwdriver, some phenomena, such as unstable fixation, whole rotation of screwdriver and unstable central axis, commonly appear so that the rotation of screw is inconvenient.
The front and back handle of screwdriver can separately rotate.
Rotate
The palm holds against the back of screwdriver to put the pressure on screw, and the screwdriver and the central axis of screw are in a straight line, while rotating the front of handle to steadily rotate the screw.
Tighten
After rotating the screw, screw the back of screwdriver to drive the whole screwdriver in order to better force and tighten.