Category Archives: Metric Aversion

A Hole in The Screw Head

Posted on by

By The Metric Maven

Thern is a friend who is a mechanical engineer, and has taught me much of what I know about  the mechanical arts. I spent a considerable time trying to learn how to use a common CAD program for drawing, but managed to get nowhere fast. I had purchased a book, but to no avail. Thern looked at my struggles and said “They’re aren’t any good books for this, but I’ll bet I can have you drawing in an hour.”  He was correct, and it opened an entirely new world for me. Thern had me draw all the component parts and then, most importantly, had me fit them together to make certain they  did not interfere. He showed me how to allow for clearances and other important information. When all the the parts for the design arrived, and they all fit together perfectly, it was sublime.

I became more and more confident about creating my own mechanical drawings for my electrical designs. Unfortunately confidence does not beget knowledge. I took the drawings over to Thern, who was actually favorably impressed by what I had done. But he noted one detail. I had holes in the design through which fasteners were to pass. They were dimensioned in decimal US Anarchy Units, as was the entire design. I do not recall the hole size, other than it seemed like a “nice round number.” Thern pointed out that if I left the nice round number on the drawing, the machinists would take me at my word and either machine the hole exactly, or obtain a custom drill bit and drill the holes. One should always look up a standard sized drill bit to avoid the extra costs. Thern cited a “standard” sized USAU drill bit, which I then called out on the drawing. Thern then told me “don’t feel bad, you have no idea how many mechanical draftsmen/engineers don’t bother to call out sizes that fit a standard drill bit.”

It turns out that in US Anarchy Units, standard drill bits are a bit difficult to pin down. What I mean is that one has to admit that a great thing about USAU is that there are so many “standards” from which one can choose.

The first standard is Fractional-inch Drill Bits. According to Wikipedia:

ANSI B94.11M-1979 sets size standards for jobber length straight shank twist drill bits from 1/64 inch through 1 inch in 1/64 inch increments. For morse taper shank drill bits, the standard continues in 1/64 inch increments up to 1¾ inch, then 1/32 inch increments up to 2¼ inch, 1/16 inch increments up to 3 inches, 1/8 inch increments up to 3¼ inches, and a single 1/4 inch increment to 3½ inches.

One disadvantage of this scheme of sizing is that the size increment between drill bits is very large for the smaller sizes, 100% for the first step. The implication is that number gauge drill bits have to be used to bridge the gaps. (emphasis mine)

Another disadvantage is the convention in labeling the bits. Rather than an integral number of 64ths of an inch, drill bit sizes are written down as irreducible fractions. So, instead of 78/64 inch, or 1 14/64 inch, the size is always written as 1 7/32 inch. This can lead to confusion and mistakes unless great care is taken.

The decimal equivalents of these fractional drill bits are numbers that I suggest no one other than an idiot savant could master and retrieve for placement on a drawing. The middle paragraph even indicates there is a nudge-nudge wink-wink assumption that people know the sizes are not very complete for small sizes, and so they need to use drill bits from another standard to fill in the gaps!

The other “standard” is US number and letter gauge drill bit sizes. Again according to Wikipedia:

Number gauge is routinely used from size 80 (the smallest) to size 1 (the largest) followed by letter gauge size A (the smallest) to size Z (the largest). Number gauge is actually defined at least down to size 97, but these smaller sizes are rarely encountered….

The numbers and letters correspond in no logical manner to the diameter of the hole to be drilled. In fact, they do not even have a linear or understandable mathematical relationship. As all the sizes are generally less than an inch, I guess I don’t know why they are not called out in barleycorns.

It is my understanding that drill bits are often used to make holes through which fasteners such as machine screws are to pass. One would expect that if an actual system existed, that there would be a correlation between the fastener designation and drill bits. There is not. For instance the size of machine screws is 0, 1, 2, 3, 4 to 10. These are all gauge numbers, which means they are meaningless numbers. A number 4 machine screw has a 0.1112 inch diameter, a number 4 drill bit has a 0.209 inch diameter.

Oh, I forgot to mention that when the diameter of a machine screw is 1/4 inch or larger, it is no longer designated with an integer “gauge number,” but is then in fractions of an inch. So above 1/4 inch we have  5/16, 3/8, 7/16, 1/2, 5/8, 3/4 and more fractions. Of course modern CAD programs are in decimals, so one has to do some computations to figure out what drill size would be the closest to a desired fastener size. I’ve often wondered how much time is wasted, and mistakes made in the US because we need to constantly use fraction to decimal equivalent charts. My father has them all over his shop.

When a fastener diameter is the same as a drilled hole diameter, this is often called a “friction fit.” There is no clearance. If there is only one fastener and hole, this is not a problem, but when there are multiple holes, their relation to one another has to be very close, if all the screws are to pass through without binding. In the case of US Anarchy Units it takes some time to figure out what clearances are possible using our “standard” drill bits and fasteners.

When I finally made the decision that my Engineering Practice would use all metric, the simplicity of metric fasteners and drill bits came as a shock. My first metric-only design used M6 machine screws. M6 is Metric six millimeter diameter. I’ll bet you can guess what M2, M3, M4, and so on all mean. So to get a friction fit with an M6 machine screw, I would need to use a six millimeter diameter drill bit, which is standard. If I need a little clearance?—use a 6.5 mm drill bit.

I bought some M6 machine screws at a business who has sold only metric fasteners and hardware for years. I asked the man behind the counter “so in your experience if I drill a 6 mm hole this M6 machine screw will pass through?”

He looked at me like I was Forrest Gump and said “they’re both six millimeter. Why wouldn’t it fit through?”

Indeed, when I went home and drilled a 6 mm hole, the M6 fastener passed right through—perfectly. I can’t imagine using US Anarchy of fasteners and drill bits now, but many people try to force me. When I call out a drill hole on my metric drawings, I know exactly what values I can use, and what drill bit to call out, and what fastener will work. I can do this all without consulting any anachronistic chart. Anybody that would choose to make drawings in US Ye Olde English Units, must have a hole in their head.

Related essay:

Without Metric Threads We’re Screwed

Yes! We have no metric drill bits

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.

Extreme Tradition in Measures

Posted on by

By The Metric Maven

Bulldog Edition

I have never been crazy about the Middle Ages or Medieval Times. It makes me think of the black plague, trial by ordeal, unclean water, the emptying of chamber pots from second floor windows, and other unpleasantness that is best left in the past. Given the choice, I will take modern medicine, law, and municipal water over those offered before this century anytime. I would hope that most US citizens would feel the same way. I find it interesting that when it comes to weights and measures there is a disconnect. The US clings to a system that is anachronistic in the extreme. How anachronistic? I’m glad you asked.

For instance, we in the US use the Winchester Wine Gallon. So why is it called Winchester? Well according to Page 30 of  Evolution of Weights and Measures (EOWAM) by William Hallock and Herbert Wade (1906):

With Winchester are associated the earliest Anglo-Saxon weights and measures, and their authority as standards is said to date back to King Edgar (reigned 958-975), who decreed that “the measures of Winchester shall be the  standard.”

We in the US also proudly use the Winchester bushel for our dry goods. Despite the fact that we fought a Revolutionary War with Great Britain, and without the French and General Lafayette providing essential financial and military aide,  we might never have become a separate nation, we cling to the traditional measures used by England—-or do we?

On page 35 of EOWAM we read:

The Winchester corn gallon, as the measure is known, was employed until it was supplanted in 1824 by the imperial gallon, while its companion, the Winchester bushel, which was similarly outlawed in 1824 in favor of the imperial bushel in Great Britain, has survived in the United States.

***

On the reorganization of the weights and measures  in 1824 the wine gallon was abolished, [in Great Britain] but it was never supplanted in the United States and remains as the legal gallon. The British imperial gallon, [was] legalized in 1824…

And on page 36:

In fact, we find the Anglo-Saxon measures of length perpetuated on the same basis as is given in the statute of Edward II [in 1324], where there is a restatement in statutory form of what has since become the well-known rule that three barley-corns round and dry, make an inch, twelve inches a foot, three feed a yard (ulna), five and one half yards a perch, and forty perches in length and four in breadth an acre.

The British even updated their definition of a yard in 1824, by defining it in terms of a seconds pendulum (page 37). Despite President Washington imploring Congress to legislate and create a rational set of measures for the United States, there has been (as far as traditional weights and measures goes) no legislation up to this day. The US Metrologists were left without a rudder, which is why many US measurement decisions, like the Mendenhall Order have come from individuals who found they had no choice but to make a decision so that commerce in the US could continue without disruption. The only weights and measurements legislation ever enacted concerned appropriating a troy mass artifact from the UK for the coinage of currency This is not the common pound in use by the US today. Otherwise congress has been silent.

Below is a table of three common contemporary US measures and the traditional ones used last by the UK before metric:

Five Gallons Imperial = 22.730 Liters

The US quart is derived from the gallon, as is the pint, as is the fluid ounce. We can see that the current measures used in the US, are not even those which were revised by the UK in the 19th century. The table above illustrates just how neglected are the weights and measures of the US. This magnitude of neglect gives procrastination a bad name. By comparison, we are behind the British measurement reforms of the 19th century by 9 centuries for liquid and dry measure (as if we need both), but only 5 centuries behind them in defining length. Ten penny nails sold in the US are named from the price of 100 nails that were sold in the 15 century. So, is our set of weights and measures more traditionally British, than the British use? It looks that way to me. How on earth can we call these units US Customary? They are as traditional as British/Anglo-Saxon measures as one can get. The are not even reformed British measures. They are fundamentalist British measures. It’s as if a Renaissance Fair was tasked with providing the US with its current weights and measures. I guess it’s what makes America great—measures which are 11 centuries old for volume and weight (no mass, or other important scientific concepts back then)—and an inch from 7 centuries ago.

I’ve never liked the rubric “US Customary” for the current anarchy of US units. It gives the completely non-systematic and backward set of weights and measures a cache they do not deserve. It is placing lipstick on a pig and calling her Monique. Considering that the units we use here in the US are actually English units which are centuries old, anachronistic, and unused even by England after their 19th century reforms, I will from now on call them US Olde English Units, or Ye Olde English Units. Alternatively I may call them the US Anarchy of Units, as Sven does, which is probably more descriptive.

The British realized they had not sufficiently defined the wine gallon in the 16th century and so defined it as 231 cubic inches. Robert Zupko on page 48 of his book Revolution in Measurement states:

In a special examination conducted by the Standards Department during 1931-32, the actual capacity of this gallon was found to be 230.824 cubic inches, a figure that would be found grossly inadequate  by today’s standards, ….

Is this what our country is? One that cannot even find the where-with-all to abandon 10th and 14th century measurement units that the British reformed in the 19th?–and who have since changed to the metric system in the 20th? The British are at least well over half-way to metric it appears. We’re still standing still—solipsistically contemplating our traditional greatness—and apparently proud to remain centuries behind the modern world.

Addendum:

To elaborate on the antiquity of our measures, the reference I quoted from: Evolution of Weights and Measures, from 1906, states that King Edgar who reigned in the  10th century decreed that “the measures of Winchester shall be the  standard.”  Queen Anne is credited with requiring this wine gallon be used by statute in 1707.  The illustration of the wine gallon shown above has that date on it.  It is also known as the Exchequer wine gallon. In 1850 the Universal Dictionary of Weights and Measures, Ancient and Modern; Reduced to the Standards of The United States of America by J.H. Alexander was published in Baltimore. Its entry on the gallon is reproduced:

The Winchester Wine Gallon is shown as unity on the right hand side. This indicates it is the standard for the US. This Wine Gallon is traced back to  the tenth century–at least, as I indicated, and is the same as the Queen Anne Wine Gallon.

The same Universal Dictionary from 1850 also states our bushel is the Winchester Bushel:

Before there was a United States, there were British colonies. The barleycorn inch was inherited from England, and when the US won its independence, this did not change. George Washington implored Congress in his first State of The Union Address on January 8, 1790 to address the weights and measures. They did not.  The barleycorn  inch was there, and used by US citizens. The barleycorn inch was introduced around 1066 AD. According to Robert Zupko the author of Revolution in Measurement 1990 (page 62):

An act of 1620 was the first to describe the foot as the length of 12 inches, even though a statute in 1685 still continued to define the inch as the length of 3 barleycorns set lengthwise. The sheer number [of statutes] unfortunately produced a difficult situation.

The barleycorn is the basis of current US shoe sizes, which I detail in my essay Brannock and Barleycorns.

One can quibble about the authority of references, but these are primary sources from the 19th and early 20th Centuries. Even NIST needs references. That we use very, very old measures, I think should be clear, and is the point of the essay.

Postscript:

The Big Bang Theory on 2013-10-24 aired an episode entitled The Romance Resonance. In it, Sheldon manages to develop a set of steps to synthesize a new stable super heavy element.

Unfortunately, Sheldon later realized that he had misread his Handbook of Chemistry and Physics.

Sheldon: I’ve made a horrible mistake

Amy: What are you talking about?

Sheldon: This table, it’s in square centimeters. I read it as square meters. Do you know what that means?

Amy: That Americans can’t handle the metric system?

It of course makes perfect sense to me that centimeters should be the villain.

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.