Strengthen your fingers and wrists: Compliments of Charles Roberts.
This device simulates the clay jar used on Okinawa.
#1: is a machine thread nut with inside diameter (ID) of 0.625″
#2: is the top of the jar and needs to be one piece. The dimension for this part is as follows:
3.70″ diameter and 0.25″ thick for the top and 2.70″ diameter and 0.50″ thick. There is a hole in the center that is 0.62″ diameter. This part can be cased or machined as one piece using plastic or metal.
#3: is the supporting shaft. The dimensions for this part is as follows: 0.62″ diameter with a length of two (2′) feet.
#4: is the base of the jar. The dimension for this part is as follows: 3.70″ diameter and 0.25″ thick.
Items #3 and #4 can be cased or machined as one piece using plastics or metal.
After machining the parts, you can place weights around the supporting shaft to the desired weight (which can be as high as 100 pounds).
Using this device, you can strengthen your fingers and wrists of your hands as well as your grip.
Mr. Roberts has kindly released this drawing to the martial arts world.