Pinch grip wrist supination (therapy putty) (Forearm supination strengthening, with putty - key grip)

Sit upright with a table in front of you.
Take a piece of therapy putty or plasticine and roll it into a sausage shape.
Hold one end with your stronger hand and hold the other end between your weaker index finger and thumb.
Twist the putty with your weaker hand by turning your wrist away from you.
Aim to keep your shoulder and body still during the exercise.