ECONOMICS: The Turn of the Screw

The U.S. and Britain are going to standardize screw threads. No great oratory attends this homely step, no military pageantry, yet it may be as important as half a dozen formal treaties.

The Americans will sacrifice their cherished Sellers screw thread profile in favor of a slightly modified British Whitworth profile, and the British will give up their 55° angle of thread in favor of the U.S. 60° angle. The agreement will eventually save millions of dollars, make cooperation in war & peace easier.

Universal & Permanent. Eli Whitney, an 18th Century Massachusetts Yankee, went broke after his cotton gin invention was widely pirated, and turned to making muskets. He got the idea of interchangeable parts. Before Whitney, each part of each factory product was different from its fellow on another product, even from the same shop. But every Whitney trigger fitted every Whitney gun. This principle of interchangeable parts became the basis of modern industry.

Obviously, it required exact and uniform standards of measurement. Lack of standard measurements messed up the trade between the American colonies; though the U.S. Constitution directed Congress to fix the standards of weights & measures, Congress did nothing about it for 80 years. Congressmen were passionately interested in the subject, but they could not agree. Repeatedly Washington begged Congress to pass a standardization law; in 1795 he suggested that the U.S. adopt the new French metric system. Jefferson thought he had a better idea: he wanted a system based on the length of a uniform cylindrical pendulum which, at 45° N. latitude, would move at the rate of one beat a second. Congress did not go for that, either.

John Quincy Adams, as Secretary of State, in 1821 begged Congress to let him “consult with foreign nations for the future and ultimate establishment of universal and permanent uniformity” in measurements. No dice.

A decade later young Sam Colt ran away from home and, aboard a ship bound for India, whittled the wooden model of a pistol that was to become the great Colt revolver. Sam did not (by 200 years) invent the revolver, but when he got into production he extended Whitney’s interchangeable-part system in the direction of the present-day assembly line.

In 1866 Congress finally got around to its duty on measurements;’it backed into the subject by defining a meter in terms of inches, although it had never (and has not yet) defined an inch. Its definition of the meter was inaccurate in terms of the British inch, so when Thomas Corwin Mendenhall, head of the Office of Weights & Measures, defined in 1893 an inch as .02540005+ parts of a meter, the U.S. inch and the British inch came to differ by .000004. (This later got bargained out in an informal compromise.)

“Do You Realize?” Meanwhile, more & more things (not including international relations) came to be held together by screws, bolts and nuts. Their shape and kind were in chaos. In 1861 the Franklin Institute got together a group of engineers who adopted the design of William Sellers as the standard U.S. screw thread. Without it, the unified U.S. railway system could hardly have been built.

Britain standardized on the Whitworth thread. Sellers’ thread is flat at the top, turns in toward the core of the bolt at a sharp angle, and goes through a flat valley at the bottom. Perhaps the less precipitous and more urbane British character accounts for the fact that the Whitworth thread is rounded, top & bottom, Anyhow, the two don’t fit.

In World War I, this was a source of great inconvenience. In World War II it was nearly a calamity. By 1943, 2,000,000 tons of U.S. steel was going into nuts, bolts, screws and rivets. A B-29 has 225,000 bolts in addition to 250,000 rivets. If a nut fell off it had to be replaced by one from the U.S. All Birmingham and Sheffield could not make its twin.

William L. Batt, when he was in charge of international supply for the War Production Board, cried out: “Do you realize that in many cases British and American gun parts are not interchangeable even though the completed products are of identical design? Can you picture the vast stocks of duplicating parts we have been forced to maintain in the far-flung war theaters because our screws were different? . . .”

Representatives of U.S., British and Canadian industry, meeting off & on since 1918, have finally hammered out a screw thread agreement in principle and expect to sign it next month.

Much is left to do before John Quincy Adams’ dream of uniformity in measurements is achieved. The U.S. is still using the Queen Anne gallon, which the British abandoned long ago. Tons are different and so are bushels, and the Japanese picul (for measuring grain) means one thing in a seaport and something else inland. In these matters, as in other aspects of social integration, the world moves slowly.

Nevertheless, as Galileo did or did not mutter, it moves.