To do the tasks using this kit, coordinated use of both hands is essential.
In this way the pressure of the thumb and index finger oppose the pulp side of the palm. 

This grip also coordinates the flexing gripping muscles of the first phalanx of the thumb: short flexor, first palm interosseus, and short abductor. The various shapes of the head of the screw varies the degree of ease and stability of the grip.

There is also a two-handed task, in which one hand acts to secure the screw, while the other is involved in a rotation task to tighten / loosen the bolt.

This aid has 5 different peg head shapes for various levels of difficulty of gripping using the fingers.