This is my first Instructable. Mostly to learn how to create and publish an instructable, but, in this case, to also have some fun.
You need some novelty handcuffs, a rubber or tennis ball. Any type of ball that can be drilled should work. It also needs to be big enough to be cuffed.

Step 1: Drill a Hole.

Since the thumb is too small to be cuffed by a typical pair of handcuffs, you need to add some size to it. I found a rubber toy ball works, but I also think a tennis ball would work. Whatever type of ball you use, it need to be something you can drill in to.

Drill a hole to hold the thumb. In my case, it required a 3/4 inch hole. But, if you are making these for someone else, then you need to use the size drill to fit their thumb.

Be careful not to drill all the way through the ball. If the tip of the thumb can be stuck out the other side, it can be used for texting.

Step 2: Test Fit.

Test the fit. It should be snug, but not too tight. You don't want to cut off the blood circulation to the thumb. This is the main reason Thumb Cuffs are not used anymore. And yes, there are really thumb cuffs that use to be used by law enforcement.

Step 3: Place Handcuffs and Ball on Hand an Cuff

Place one side of the hand cuffs on the wrist and adjust. Place it so the lock mechanism/chain are on top of the wrist. Put the other side of the handcuffs around the ball. Adjust the cuff so it is snug around the ball.