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.
The advantage of the nutcracker shown in the illustration is that it can be adjusted to various-sized nuts. The handles are similar to those usually found on nutcrackers except that they are slotted at the cracking end to receive a special bar. This bar is 2 in. long, 1/2 in. wide, and 1/8 in. thick, with 1/8-in. holes drilled in it at intervals to allow for adjustment. Cotters are used in the holes as pins.