I first got the idea for this from an article by Michael Clarke in Blitz Magazine, and have since refined it after purchasing and reading his book "Hojo Undo - Power Training for Traditional Karate" (a book I would highly recommend, by the way).
It's a wrist and forearm conditioner. You hold it between the hands, and roll the weight up, then down. After 2 or 3 times doing this, while trying to keep it steady, you can really feel it working. I use it with hands in the sanchin ready pose, both palms up and palms down, which gives the shoulders and lats a bit of a workout too.
Construction was from a scrap of 30mm Mountain Ash dowel I had lying around, some 4mm polypropelene rope and 5kg in dumbbell weights. A hole drilled through the dowel, and voila, a makiage.
The makiage is one of my favourite tools, probably because I like to get close and offbalance/interrupt my opponent by grabbing and pulling, pushing or turning.