Forearm Roller Exercise
As you can see it is fairly simply to make one, juts gte a bit of dowel wood approx 2 inches thickor more, drill a hole through and centre and put some sturdy string through it (or you can try fishing wire), start off with a 5kg weight on the end. Keeping your elbows locked to your sides and arms directly in front of your elbows, palms facing down, hold the roller and roll the weight up to the top, then down till it's nearly touching the floor, try and do this for a few reps (3+) - you'll be amazed how quickly you progress, I was lifting 20kg within a month.