When PigFish Fly

Dr Clayton Forrester Creating a PigFish

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.

The International Space Station — PigFish In Space

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.

“Hey Fruit Loops. Are the tools needed imperial or metric?”

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.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.

The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.

The third book is not of direct importance to metric education. It is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.

7 thoughts on “When PigFish Fly

  1. “Every country is somewhere in this process of going metric, some much further along than others.”
    Source and further information:

    Burma use traditional measurements, in daily use, that can be expressed by S I equivalents, as well as British Imperial units. However their government has moved towards adopting the S I units as well as Malaysia in that region for economic reasons since 2008.

    Liberia was established by citizens of the United States, as a colony for former slaves. Between 1821 and 1847, by a combination of purchase and conquest, American “Societies” developed the colony “Liberia”. On July 26, 1847, it declared its independence. http://en.wikipedia.org/wiki/History_of_Liberia As a country it does share US customary units of measure.

    The National Bureau of Standards (NBS) made the metric system its standard back in 1964. Since then our Customary Units in the United States have been pegged to the S I Unites. At present we know a metre is divided into 1 000 mm. What most people do not think about is that 1 yard is defined as 914.4 mm, 1 foot is 304.8 mm and an inch is 25.4 mm.
    My main point is that products put together with inch-mm combinations have a metric unit base. My other point is we in the US have to rethink about shared status when referring to Burma, Liberia, Jamaica, and other West Indies Islands.

    • The main problem in engineering and manufacturing is the inch and millimetre don’t convert well into each other resulting in a mess of decimal dust, requiring some rounding and a slight loss of precision.

      For whole numbers, it would have been better if the inch was defined as 25 mm instead of 25.4, but for fractions, the inch would have worked better with 25.6 as the converted result would have been either rounded millimetres or to one decimal place.

      A 24 mm inch would result in millimetres in increments of 1.5, thus inch products made decades ago when expressed in millimetres would have resulted in more rounded numbers and it would have been impossible to say whether the product was intended to be in millimetres or inches. It could have been made either way and still been simple to make by either side.

      But now with almost everything being made to rounded millimetres, inch users have to deal with inches that are not only conversions but rounded much more then what is acceptable.

  2. Can you provide some type of proof that the imperial units are used in the US? I buy gasoline by the USC gallon. I asked the attendant at a local gas station if they would sell me in imperial gallons. He had no idea what I was talking about. I told him that there is a person who insists that in the US we use British imperial measures which uses a larger gallon. If this is true, then why can’t I buy gas in imperial units? The attendant didn’t know.

    When you tell people your weight, do you use imperial units? If so, what reaction do you get when you tell them you weight using stones? What? You don’t use stones and don’t even know what they are? How can that be? Stones are imperial. Those who use imperial use stones, those who use USC use only pounds.

    Why don’t you know the difference?

  3. As far as I know, there are no imperial tools used on the ISS. For the American contribution using inches, they would use inch based tools for UNF or UNC fasteners, which are not imperial. Imperial had its own fastener series, called Whitworth. Unless someone can prove otherwise, I’m going to believe that there are no imperial Whitworth fasteners used on the space station. Imperial Whitworth fasteners basically became obsolete when the UK went to metric ISO series.

    Calling USC as imperial is what the UK metric haters prefer. It makes them feel that they are not alone in using imperial units. They know there is a difference, but they also know most Americans don’t know there is a difference and play on that ignorance.

    Again there is no imperial used on the ISS.

  4. One thing that can be said about themetricmaven’s information about the ISS and NASA is that it is dated.

    He should look to what is in store for the ISS in the future, not what happened in the past. Check out the Wikipedia website:


    and scroll down to:

    End of mission
    According to a 2009 report, RKK Energia is considering methods to remove from the station some modules of the Russian Orbital Segment when the end of mission is reached and use them as a basis for a new station, known as the Orbital Piloted Assembly and Experiment Complex (OPSEK). The modules under consideration for removal from the current ISS include the Multipurpose Laboratory Module (MLM), currently scheduled to be launched in 2014, with other Russian modules which are currently planned to be attached to the MLM until 2015. Neither the MLM nor any additional modules attached to it would have reached the end of their useful lives in 2016 or 2020. The report presents a statement from an unnamed Russian engineer who believes that, based on the experience from Mir, a thirty-year life should be possible, except for micrometeorite damage, because the Russian modules have been built with on-orbit refurbishment in mind.[285]

    As you see, the Russians plan to decouple their modules from the space station and create new station with them. So, can you guess what will happen to the rest? What happens to the rest, I can only speculate, but I can tell you NASA is not getting the funding it needs to continue support and it looks like the American module will end up in a decaying orbit to burn up in the atmosphere.

    According to the Outer Space Treaty the United States and Russia are legally responsible for all modules they have launched.[286] In ISS planning, NASA examined options including returning the station to Earth via shuttle missions (deemed too expensive, as the station (USOS) is not designed for disassembly and this would require at least 27 shuttle missions[287]), natural orbital decay with random reentry similar to Skylab, boosting the station to a higher altitude (which would simply delay reentry) and a controlled targeted de-orbit to a remote ocean area.[288]

    NASA pissed off a lot of people in aerospace with its decision to design the Constellation in inches against the advice and desire of everyone else involved. These companies had no choice but to go over NASA’s head and have President Obama cancel Constellation. NASA today is becoming nothing more that an organization that allocates funding to companies like Space-X and Bigelow Aeronautics who will do all of the design and construction in metric.

    In the past NASA may have been forced to use USC due to pressure from the contractors who did the actual work. But private companies aren’t under that pressure. A sub-contractor that has a problem with using metric is blacklisted and doesn’t get a contract and there is no one to complain about it.

    All the metric opposers can do is yak on what NASA did, but either they are unaware or or refuse to believe that NASA and its attraction to inches is on the way out. The handwriting is on the wall for NASA and any future space projects will involve private companies engineering, designing, manufacturing and servicing in metric.

    BTW, NASA did use the metric system in the days of Werner von Braun. He once stated before his death that he loathed USC and used metric in his calculations, as did the other Germans working at NASA pre-1970s. They were forced to convert their results so that the contactors working in inches could build the rockets. So in essence it was the hidden metric that put man on the moon and USC stole the spotlight.

  5. “When confronted with this farrago of parts, an American gesticulating with his gill of grog in hand might state”

    (Mind Blown- I’m stealing this quoate)

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