Recently I watched a man trust his life to the threads of a bolt. His name is Noah Bigwood, he's a world class climber, who can scamper up a rock face that looks like a shear vertical slab. I met him while he was guiding my wife and some of our friends on rock climbs in Moab, Utah, although he didn't guide me because dangling from a bolt on a cliff isn't my idea of fun.
This fact makes recreation climbing, then, a hobby made possible by the Industrial Revolution of the 19th century. We can still see the fruits of 19th century thread design in today's bolts. Go to a hardware store and pick out a large bolt and look at the bottom of its thread. You'll notice that it is flat and not pointed like a Vee. It is this flatness at the bottom that is a key to mass producing a bolt.
Mass production was partly driven by the needs of railroads. As they spread westward locomotives were often repaired hundreds of miles from the central shop, thus the bolts used for repair had to be uniform for interchangability. To be uniform required a standard system. At the start of the Industrial Revolution the English system prevailed. These bolts featured threads that came to a sharp point at the bottom. These bolts worked just fine, yet they could not meet America's need to fill the world with mass produced objects. This simple English screw was too complicated.
To make the very sharp vee-notch of the English screw took an expert machinist using five different machines. In Britain this worked well because there was a surplus of labor; but in America, which was expanding in leaps and bounds, there wasn't enough highly skilled labor available. In response to this William Sellers, America's pre-eminent tool-maker, designed a bolt thread able to be made not by experts, but by "all good practical mechanics."
Sellers' improvement was extremely simple: He flattened the bottom of the Vee thread. This simple redesign allowed the bolt to be made easily by any component machinist.
That flat cut at the bottom is engineering at its best: It isn't some fundamental scientific principle, it isn't even artistic. Its just good, practical engineering that makes possible just about every mass produced object - including the bolts used for climbing mountains.
Copyright 2001 William S. Hammack Enterprises
