Grip a sledgehammer or plate-loaded dumbbell with weights only on the top side and hold it vertically in front of yourself with your elbow bent to 90 degrees and forearm horizontal.
 
Slowly rotate your hand in each direction as far as possible. The closer your grip to the weight, the easier the movement.
 
Purpose
The sledgehammer wrist rotation strengthens the wrist and elbow.
 
Programming
Generally sets of 10-20 reps are appropriate. Slow eccentrics often help more with rehabbing various elbow issues like tendinitis or strains.