This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
To strengthen a weak wrist, take a piece of leather, preferably white oak tanned, 2 in. wide and 14 in. long, and carefully shave it down with a sharp knife, until it is 1/16 in. thick. Then cut it as shown in Fig. 1, the wide part or body being 7 in. long, and the narrow part or neck, 6 in. long and 1 in. wide. Cut a semicircular hole, 1 in. from the extreme end of the body, 1/2in. wide and 1 1/4 in. long, to allow the neck to slip through, then punch three holes in each end and lace with rawhide or shoestring, or, better still, if you happen to have a small buckle, sew it neatly to the body. It looks better