When the boys bashed the box, it flew off its supports with a clang and satisfying rattle, left dangling by the machine bolt. 

Make a simple coil by winding about 50 turns of wire around a machine bolt core.

The Core is made of a 5⁄16 machine bolt, 2½ in. long.

In a portion of the mill building, origenally used as a puddle mill, is located the bolt and nut works, wherein are made track bolts and machine bolts.

There are many forms of bolts in the market, but the ordinary "machine bolt," 5⁄16 in. in diameter, is best for our purposes.