Spiral Torsion Springs
Spiral torsion springs are normally used in applications requiring less than 360 degrees of rotation. They are generally used to obtain a large amount of torque through a small amount of rotation.
The torque available per revolution is linear for the first 360 degrees. If the deflection is greater, the coils often "close out" or come into contact with each other, causing the torque to rise rapidly. John Evans' can offer various details to attach the end of the springs.