A Hole in The Screw Head

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.

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Related essay:

Without Metric Threads We’re Screwed

Yes! We have no metric drill bits

The Magic Infrastructure

The Sewer Urchin — The Apotheosis of Cool

By The Metric Maven

Bulldog Edition

Any sufficiently advanced technology is indistinguishable from magic.

Arthur C. Clarke (1917-2008)

I still recall when I was too young to reach the kitchen faucet. I would have to ask my mother to draw a glass of water for me to drink, and wait to grow. I grew up with access to water on demand. I could flip a switch and summon light. The house was warm in winter and cool in summer. The seemingly most important of all the things which provided comfort, was the ability to turn on a television. I took it all for granted as much as there would be oxygen in the room for my next breath. Indeed as far as I knew, it was all based on magic—without cost to anyone.

One Winter the twin lead cable from our television to the antenna on the roof snapped in an ice storm. The image on the television screen disappeared and was replaced with “snow.” The name seemed very ironic. It would be a couple of weeks before the ice on the roof melted sufficiently and allowed my father to reconnect the antenna. Life without television had become unthinkable, and its absence almost unbearable. It was my first experience with the loss of “infrastructure.” The failure began to make me curious about the origin of water and electricity. When I truly realized that somewhere coal was burned to create steam, which in turn rotated an electric generator, and provided electricity it surprised me that it was available 24 hours a day. But like many Americans, I began to take it all for granted and gave it little thought.

My Grandfather had a small cabin in the backwoods of Montana where he often spent weekends. The cabin was made of logs and only had a wood stove, and cabinets for food storage. The nearest electricity was 27 kilometers away. An outhouse was conveniently located about 10 meters from the cabin. We obtained water from a nearby creek. It was quite an adventure with wildlife all around, the smell of lodge pole pine in the air, and the multitude of stars one would see in a night sky without light pollution was sublime. A single gas mantle lantern illuminated the interior where we both read books into the night.

It was all very pleasant, but after a couple of days without a shower, or running water, or indoor plumbing, or electricity, or a telephone, it was nice to know I could quickly return to a home with modern infrastructure. The weekends offered solitude and relief from the modern pace of life, but also provided considerable respect for why our ancestors created infrastructure in the first place.

As a boy, I survived an F5 tornado passing over my grade school building. When I was evacuated, not long after the tornado had passed, the phone lines, power lines, trees and all the infrastructure of the small town in which I resided was devastated. There was no electricity for 1-2 weeks as I recall. The water wasn’t safe to drink. I stayed at a relatives house while the infrastructure of my little town was re-built. For months afterward the sounds of chainsaws and the movement of utility trucks was a constant.

Path of F5 Tornado

My interest in American infrastructure was greatly rekindled when I listened to a lecture by Scott Huler,  and later read his book On The Grid. What intrigued me was how oblivious I was to it all. When most people I know talk about infrastructure, it’s  usually to complain in some way. My Uncle used to quip: “There are two seasons in Minnesota, Winter and Construction.”

Since my youth, I had seen multicolored spray paint on road surfaces, but gave it little thought. Huler provided a “decoder ring” for the colored lines, which are standard throughout the country. Reviewers of Huler’s book have noted with annoyance that it is a book without any illustrations. I can agree with their sentiment, but he provided a useful Infrastructure Rosetta Stone with this graphic:

Each color of spray painted line, defines the path of Gas Lines (Yellow), Water Lines (Blue), Sewer Pipes (Green), Electrical (Red), Communications (Orange). When the path enters a lawn, small plastic flags with the same color mark the path across a lawn. White lines indicate the excavation limits. When you see these colored lines appear, you can be confident that construction will follow.

The colors indicate the area has been surveyed. As discussed in a previous blog, surveying is still done in chains, even though the most important advance has been the use of GPS, which is meter based. The GPS metric units are all converted to chains and feet by the surveyors. When an area is leveled with bulldozers, GPS is again used. Huler’s book illustrates the undisciplined way we use measurement:

Survey of Australian Subdivision in Metric

“We have an alarm that will flash on the screen if you are getting out of tolerance. I think we have it set at 2/10 of a foot”—that is less than 3 inches. If that’s not enough, there’s a system called Millimeter GPS made by a company called Topcon. “We can measure to the nearest millimeter today.” (page 18)

How about we just use millimeters? The alarm is set to 60 mm, and it’s possible to measure to the nearest millimeter today.

The way we channel storm water has decreased the amount of fresh water that returns to the water table. It instead shoots down storm drains into rivers and ends up in the sea in a short period of time. To mitigate this problem, Civil Engineers have been adding back meanders and have slowed down the flow so that more fresh water is retained. Scott Huler spends a considerable amount of time tracking down the path water takes in Raleigh, North Carolina. Here is how he describes the water flow with imperial units:

A USGS stream meter at the park later allowed me to retrieve only the value of the flow I was wading through: It was about 4/100th of a cubic foot (about a third of a gallon) per second, which is about 20 percent below it’s mean value over the last 12 years.(page 49)

Let’s convert this over to metric and see how it reads:

A USGS stream meter at the park later allowed me to retrieve only the value of the flow I was wading through: It was about one liter per second, which is about 20 percent below it’s mean value over the last 12 years.

The actual value is about 1.13 liters, so he could have also said that or 1130 mL. but the value seems too precise with the caveat of about attached twice in the original, so I just rounded it to a liter. I’m sure Scott Huler reported with values the USGS provides, and until we can change to metric, we will be collectively stuck with multiple inarticulate measurement units. Another example is:

Raleigh gulps as much as 50 million gallons of water per day, which require the intake to suck out 80 cubic feet per second. (page 54)

Which could be written in metric as:

Raleigh gulps as much as 200 million liters of water per day, which require the intake to suck out 2000 liters per second.

Then Huler leads into part of what the thesis of this blog is about:

There are O-rings for hydrants (they all have the same thread; there’s a plan to eventually adopt a nationwide thread so that all the hydrants will have the same connections)……….(page 68)

The National Bureau of Standards was created because of The Great Baltimore Fire which occurred on February 8th, 1904 (1904-02-08). Fire Departments from nearby cities were called, but when they arrived, none of their hose fittings were compatible with those of Baltimore’s fire hydrants, and so the fire kept burning as if they had never shown up. We have had 108 years to solve this problem, but like metric, nothing has happened. Perhaps because it’s all voluntary?

“Together we stand, with shovel in hand, to keep things rolling along” — Ed Norton

The physical infrastructure of the United States is crumbling. This seems to be acknowledged by our citizens, but its implications are not truly understood. Our lives are rich beyond our historical understanding. We have clean water with which we can drink and bathe. We have sewers to remove our waste and waste water. We have an electrical grid which powers all our electrical equipment and natural gas lines which act as an alternative to electricity for cooking and heating. Our communications lines have interconnected the planet. We also have roads, and bridges that allow for transportation, but as Huler points out, a most important part of our infrastructure is in complete disrepair—our railroads.

The era of inexpensive oil is over, and climate change is already accelerating the deterioration of our infrastructure. Most of the world understands this. The obvious response is to build high speed rail in the US so that people may be transported in a more cost effective manner. Transportation is the life blood of a modern economy. If it is not preserved, then an economy will slow and wither. It is important that we construct high speed rail in the US in metric, this will decrease costs for us, and employ Americans to build them, but moreover it would also make our trains ready for sale to international customers. With 95% of the worlds population using metric, it would be foolish to construct trains that required imperial tools for maintenance.

The difference between a nation and a free-for-all is universal access to a common shared infrastructure. The United States has a choice, to rebuild our infrastructure and remain a great nation, or to accept a regression into feudalism with the limit being The World Without Us. The Roman aqueducts and infrastructure did not crumble in a day, and nor has ours. It, like Rome will not be rebuilt in a day either. According to Huler: “China Spends 9 percent of its gross domestic product on infrastructure, Europe spends 5 percent.” The US had decreased from 3 percent to an anemic 2.4 percent. In Huler’s words: “People persist in believing that these systems will somehow maintain themselves, expand themselves, improve themselves without anybody having to put anything in.” There seems to be a considerable number of Americans that believe our infrastructure runs on magic, but it doesn’t, it runs on eternal public vigilance and funding.

The cost will be very large. In 2008 The American Society of Civil Engineers estimated we would need to invest at least $2.2 trillion over five years to bring our infrastructure back from the dead. How would taxpayers feel if I told them I could give them a 10-15% discount on whatever amount we spend on infrastructure?—forever. I suspect they would be for it. It is proverbially known that changing the US over to the metric system as part of a plan to rebuilt our infrastructure, would save at least that much in construction costs. Ten to fifteen percent on $2 trillion dollars is a serious savings.

An overhaul of our infrastructure would be a great opportunity to reform our domestic industries. We could implement metric threads and dimensions for the new pipes, standardize sheet metal thicknesses to metric, reduce the number of fasteners we would need by using all metric, and implement other useful reforms. A metric infrastructure overhaul, would create a workforce well acquainted with building in metric. This in turn will allow our international building contractors, who continue to cling to ACSOWM (i.e. inches, feet etc), to directly bid metric construction projects in foreign countries.

A coordinated metric conversion across all American industry during the repair and upgrading of our infrastructure could bring a sense of national unity. We could tap an American esprit de corps with the rebuilding of our infrastructure and society, and reverse the increasing ennui among the public. I can only hope We The People can find within ourselves, the will and drive to engage in this essential undertaking. For as Benjamin Franklin said: “One never knows the worth of water until the well runs dry.” Let’s not wait for that moment to act.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page.

Related Essay:

The Invisible Infrastructure