By The Metric Maven

Bulldog Edition

The lack of any weights and measures reform in the US has created an odd situation. Both Imperial and metric parts often make their way into US product designs. This metric advocate has called this situation where metric and imperial are mixed—often on the same part—PigFish. It makes as much sense as sewing the head of a pig on the body of a fish and expecting something good to come out of it.

Recently I needed to purchase a house fan. After returning from the store, I discovered to my surprise I had to assemble the base. I was not prepared for that, or the associated drawings.

In Figure 2, there are two screws called out as #8 x 3/8″. I have written about the absurdity of imperial screw threads in previous blogs. This is a #8 “gauge” screw which is 3/8 inch in length. So far this is not untypical for an American made product. The screws fasten the two halves of the fan’s plastic base together. Then in Figure 3 we are to attach the base to the fan itself. The screws to accomplish this are designated as M5 x 1/2″! This is serious PigFish. A screw with 5 mm thread is called out as having a length of 1/2″. Metric and imperial on one part!

The mixture of imperial and metric fasteners in the US wastes an incredible amount of time, yet is invisible to most people. As an example, my father often works on equipment at a printing company. One day recently he had to work on a piece of broken equipment. He noted it was manufactured in the US, and therefore assumed that it was imperial. He went and obtained imperial wrenches, only to discover when the tools didn’t fit, that it had been designed in metric. The situation becomes much more complicated in the only country in the world which has no aversion to using both metric and imperial in the same product. One needs two sets of tools to support this absurdity, which increases the cost of tools in the US needlessly. When a product incorporates imperial and metric randomly—working on it becomes a guessing game which further wastes time. I have no idea how much this costs when added up in a nation the size of the US, but it makes it easy to believe the estimate that non-metrication costs each person in the US $16.00 per day.

My Father received an outdoor grill as a gift this last Summer, and when putting it together, noted that metric and imperial were again mixed and matched. There are 1/4″-20 x 3/4″ screws with #8 x 3/8″ self tapping screws and 7 mm lock and flat washers with 1/4″ nuts.

When confronted with this farrago of parts, an American gesticulating with his gill of grog in hand might state: “Well all you’ve shown me is a couple of small items, where the parts are all provided, it’s no big deal.” Well then, let’s explore the potential danger created when PigFish fly.

Michael Milstein wrote about this problem in the March 2001 edition of Air & Space magazine. He notes:

…..the U.S. portion of the International Space Station is built in Imperial Units while the

rest of the super-expensive structure has been constructed in metric. About 10 years ago NASA gave serious thought to the idea of building the whole thing in metric, but decided that would drive the cost way up. All the NASA contractors were tooled to build parts in inches and pounds; converting to metric would have required revised designs and new machines. So instead they developed an elaborate and costly computer-modeling and cross-checking procedure to make sure that metric and Imperial parts fit together and work properly.

I’m not convinced NASA ever gave any serious thought to building the US part of the International Space Station (ISS) in metric. Milstein further relates:

Right now the Russians are controlling the space station, figuring propulsion exclusively in metric units. Once the on-board laboratory (expected to have launched January 18) is up and running, the U.S. will take over control exclusively in Imperial units. When I asked spokesman Kyle Herring of NASA’s Johnson Space Center in Texas what would happen if there were some confusion between the two, if a maneuver supposed to be carried out in pounds of thrust were actually done in kilograms or the other way around, he explained that the station’s propulsion system operates at such low thrust that even a major miscalculation couldn’t send it spiraling into the atmosphere.

It is quite surprising how sanguine NASA is about the ISS, when the Mars Climate Orbiter, and the DART Satellite, both had “mission failures” because of metric/imperial conversion problems.

I recently attended a social function where I met a woman who has a PhD in Mechanical Engineering. She and her husband had both been involved with the ISS. He is a metric advocate, and along with a number of other Engineers lobbied hard for metric only construction. They filled out the numbing amount of paperwork and invested time to make the American part of the ISS metric. The request moved upward, and then tumbled back down with a NO attached. Why do we continue our self-imposed technical segregation from the rest of the world? In Aerospace one never knows just who makes this decision, it just moves down through the bureaucracy and splats on your desk.

What really struck me was the consequences of this choice. When the astronauts on the ISS need to make a space walk to repair or work on the ISS, they must take both metric and imperial tools with them. Strange we can justify two sets of payloads, rather than using metric exclusively. I was gobsmacked at the choice to allow imperial with metric. Because there has never been any compulsory metric legislation in the US, our astronauts must have two sets of tools to work on their equipment in space, just like my father has to at his print shop. We also impose this need for dual tools on the astronauts from other countries, which are all metric. Milstein sums up his view of the US:

We’re like a crotchety old hermit. The rest of the international neighborhood works together and speaks the same language while we huddle in a dark, outdated house at the end of the street (which we share with Liberia and Burma, the only other two nations that have not gone metric), mumbling our own inscrutable tongue of inches, feet, yards, miles, links, rods, furlongs, pecks, bushels, bolts, barrels, fathoms, leagues, acres, ounces, pounds, tons, cups, bales, pints, tablespoons, gallons, hands, chains—most of which have no logical relationship to one another—and all the other aged terms of what is often called the Imperial, or English, system…..

When will we become metric in the US?—unfortunately it may be only when pigs fly. To our great misfortune, and hubris, PigFish have already.

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