Since when did 3/8" = 9.2mm?

Beano

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You'll be short changing yourself if you accept anything less than a 308.4 mm sub..:cool:
 

seasink

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I have never used centimetres, always mm since the 70s, and no shopkeeper has ever scratched his head or called me out. Try it. Perhaps the number of building tradies about has made them familiar.

I drove a car with an mph speedo for 30+ years after metrication. You become quite adept at converting to kph without further thought. 0.62 is the factor from kph, but 0.6 is easier mental arithmetic. So a signposted 80 becomes 48 which leaves a small camera safety margin.

Those who drove pre-metric would consider 50 mph to be a slow trip on a main road, and cars were far inferior then.
 
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schlitzaugen

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The imperial system was widely popularised because of the strong development of the oil industry at the turn of the 19th century when mostly American companies manufactured all the drill rods and piping and also because American companies were the most advanced in oil exploration and extraction. I come for a profoundly metric system place but as a geologist I had the imperial system implanted in my head starting in about third year at Uni when I started all sorts of engineering units taught by old professors with vast experience in the industry. Some had actually worked with the Americans before WW2 when they came over to kick start the oil industry. These people were so archaic, they still used engineers' rules even though computers were already making serious inroads and small palm calculators were everywhere. They believed it was shameful of an engineer to not be able to quickly do sophisticated calculations in the field. I dug out my father's old rule and tried to get on with it but never got far enough to compete. I am still amazed by people who can work with the slide rule faster than typing on a calculator but I think they're getting thin on the ground. These days I use shortcuts as described by seasink for quick mental calculations. Fractionals are another problem but I can approximate pretty quickly what they are. Thou is easy but conversions from thou to fractionals and viceversa still take me a while (try this - how many thou is 3/8" ? If you can do it in less than two seconds, you're well and truly imperial minded, now say it in millimetres).

The tradition of imperial units persists in the industry and manufacturing everywhere I know of is still in imperial sizes for anything to do with pipes and drilling. All the workers I have met and worked with overseas (and here, of course) in the industry still talk inches (or sometimes "zoll" /tsɔl/ as inherited from ze germans) when talking about anything to do with drilling/piping and switch seamlessly to metric units when they talk anything else so phrases like "we need to go five inches to a depth of 360 metres and then switch to four" are nothing unusual.

One really annoying side effect of all this mess is the modern machinery coming out of China where they probably copied old English machinery and then they slapped graduated scales in metric units without changing leadscrew threads from imperial. The result is that you might take a cut of say 1mm but when you measure you realise it is in fact 40 thou, which is just over 1mm and you scrapped your part. Not all have this problem, so you need to check your machine before you use it.
 
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driven

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Just go to USA, they do not have this issue.
They in fact bombed the Renault factory in France during WW2 to stop metric.
French tried metric size tyres, look where that went, the same as BETA recorders
 

schlitzaugen

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The reality is that imperial is metric. Before the metric system, there were a number of different inches and I am not sure people using the inch even knew that. Today the standard everything is referenced to including the inch is the metre. Which makes the inch a derived unit.

To their credit, the US is metric by law. Everything government is metric. A lot of people in the US actually have no problem, but like the oil industry most have no reason to go metric. The oil and tyre industries operate in their own realm, which doesn't really impact anything else and it doesn't make any sense to change. Their tooling and everything is already set up and given that the car doesn't care how you measure its tyres or the pipe its diameter I would say they won't change any time soon. This is the same in every other country where tyres and drilling material is manufactured and nobody has a problem with that.

There's a different story when you buy cheap tooling for your home shop and find that a metric collet or drill bit is in fact just an imperial size with a different label.

And a side note, they have a much better range of metric fasteners than we do. If you don't believe that, try to find M7 socket head screws/bolts here.
 
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seasink

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I stopped using a slide rule for income-earning work years ago. Now you have gone and got me to open a drawer with several of them, both straight and circular. To my own astonishment I can still do multiplications every bit as quickly on the rule as on a calculator.

I must be well versed in old measures. I had the inch to thou answer instantly. (We once spent a lot of primary school time in this state memorising fractions as decimals by rote)

Older construction engineers are quite happy to talk in mixed systems too. It confuses the young.
 

seasink

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One of these. Most were about 5 inches across, but I have a large diam model, so about two to three times the length and accuracy of a standard rule. A 10 inch one was a computer! There is a collection here: https://www.sliderulemuseum.com/Circular.htm

All are inscribed with logs to base 10, most have tangents, but there are others with built in formulae that only needed input. Both sides are engraved.

I used a mathematical rule with several functions including roots (only the ordinary log scales.divided by two and three)

In the pic you can't see that the scales are inscribed on concentric wheels.' Concise brand were student cheapies with a flimsy cursor that could slip. This one has squares and cubes on the inner scales, then reciprocals, then standard decimal numbers on the rim.
circular slide rule.jpg

This is set to divide 18 by 25 on the outer scales. Answer at top, opposite the black 1 pointer = .72
Doing a further multiplication, say by 3, then opposite 3 on the inner scale is the answer on the outer = 2.16
You can mark that with the cursor if you want to keep calculating. The user has to keep track of the decimal point.
 
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fritzelhund

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Some years ago owned a VS Commodore, the V6 engines needed regular water pump replacements , probably due to the extreme tension on the huge ( 8 feet ??? ) serpentine belt. These engines started life as Buick products in the US of A, but by VS Commodore times were built in OZ. The water pump fasteners were still imperial while the rest of the engine was metric.
 

Roger Wilkinson

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Some years ago owned a VS Commodore ... The water pump fasteners were still imperial while the rest of the engine was metric.
We can do better than that! Slough DS19s had a lot of Whitworth and BSF fasteners as well as the French metric fasteners (according to the old 1930 French standard).

Roger
 

Greenpeace

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My nut and bolt shop has a good range of M7 bolts and screws as they are fairly common on Japanese bikes, M9 on the other hand.🙄 They also keep most common sizes of BSF. My 1924 Douglas motorcycle had 9/32" x 25 tpi threads for the chain adjusters, a request for these bolts was met with a blank look, "it is neither BSF or UNF". I ran an M7 x 1mm tap through as there was virtually no difference and they stocked M7 bolts.
Tyres have already been mentioned but I would be willing to bet more than 50% of new cars have a wheel PCD that is actually a metric equivalent of an imperial base measurement. 108mm (4 1/4"), 114.3mm (4 1/2") 139.7mm (5 1/2") etc, not to mention automotive rim widths are usually measured in inches too 17"x7" and so on. Tyre placards almost always include pressures in PSI. I don't remember ever asking a tyre fitter what pressure he put in my tyres and getting a reply in KPA or bars. I had some tyres fitted to loose rims only last week, 38 pounds was the reply.
Ask a young person how much boost they're running! What does their car run in the "quarter"? What's your 60 foot time? What size rims do they have? Young people quote HP at the wheels more often than they do KW.
Got a 4inch lift kit with a 2 inch body lift and a set of 35s on 10 inch rims bro!
Socket set, will that be 1/4", 3/8", 1/2" or 3/4" drive?
6 inch,foot long, quarter pounder, 8, 12 or 16 oz coffee?
Buy a pair of shoes based on the barleycorn system of measurement lately? Size 7 hat? Ask your wife/girlfriend her bra size!
I don't think the imperial system is vanishing any time soon, and certainly not in the automotive world.
 

schlitzaugen

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My nut and bolt shop has a good range of M7 bolts and screws as they are fairly common on Japanese bikes, M9 on the other hand.🙄 They also keep most common sizes of BSF. My 1924 Douglas motorcycle had 9/32" x 25 tpi threads for the chain adjusters, a request for these bolts was met with a blank look, "it is neither BSF or UNF". I ran an M7 x 1mm tap through as there was virtually no difference and they stocked M7 bolts.
Tyres have already been mentioned but I would be willing to bet more than 50% of new cars have a wheel PCD that is actually a metric equivalent of an imperial base measurement. 108mm (4 1/4"), 114.3mm (4 1/2") 139.7mm (5 1/2") etc, not to mention automotive rim widths are usually measured in inches too 17"x7" and so on. Tyre placards almost always include pressures in PSI. I don't remember ever asking a tyre fitter what pressure he put in my tyres and getting a reply in KPA or bars. I had some tyres fitted to loose rims only last week, 38 pounds was the reply.
Ask a young person how much boost they're running! What does their car run in the "quarter"? What's your 60 foot time? What size rims do they have? Young people quote HP at the wheels more often than they do KW.
Got a 4inch lift kit with a 2 inch body lift and a set of 35s on 10 inch rims bro!
Socket set, will that be 1/4", 3/8", 1/2" or 3/4" drive?
6 inch,foot long, quarter pounder, 8, 12 or 16 oz coffee?
Buy a pair of shoes based on the barleycorn system of measurement lately? Size 7 hat? Ask your wife/girlfriend her bra size!
I don't think the imperial system is vanishing any time soon, and certainly not in the automotive world.
Hehehehe! Yes, okay, okay. We are slow to change. Proof that tradition is stronger than government.

You've got to tell us what that shop is. When I was looking for M7 socket heads I came up empty so I had to order in the US. Found a few places over there that had everything you wanted in every length you wanted it.

But I do go by metric shoe sizes (since childhood).
 

Greenpeace

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Tractors not a KW to be seen, HP rules. Farm equipment, slashers, irrigation pipe etc, you'll have more luck finding what you want if you type in imperial measurements, (4ft slasher for example).
Boats, trailers and caravans regularly advertised in feet and often manufacturer has a reference to the length in feet in their model number. Outboards are rated in HP. Shipping containers, 10', 20' or 40' sir?
Altitude for aircraft is in feet, speed in knots (usually followed by mph in brackets in aviation literature). Aircraft measurements normally quoted in feet, wingspan etc, engine thrust in lbs. Ships speed in knots. Australian military armament is quoted by the ADF in a mix of imperial and metric, .50" cal, 5", 7.62mm etc.
Unit of blood is equal to one pint.
Precious metals (bullion) are Troy ounces.
9" diff, 4" tailshaft, 850cfm carby, 3" exhaust.
I guess it's only been 55 years since we started going metric (decimal currency 1966), no hurry.😁
 

Greenpeace

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Hehehehe! Yes, okay, okay. We are slow to change. Proof that tradition is stronger than government.

You've got to tell us what that shop is. When I was looking for M7 socket heads I came up empty so I had to order in the US. Found a few places over there that had everything you wanted in every length you wanted it.

But I do go by metric shoe sizes (since childhood).
Hi I use Porters in Toowoomba, however Nut and Bolt Australia list M7 socket heads in black (up to 40mm) and Classic Fasteners list M7 socket heads in stainless (50mm). There are also several Aust listings on EBay for M7 socket heads. Aust availability may depend on the length you were chasing though? I bought a selection of coned titanium socket head bolts, nuts and washers from the UK a few years ago as part of my lightening procedure on my Reliant Regal. It wasn't a very big bag for $160, but I did reduce the car's weight by 700g!! Titanium bolts in 3/8" and 1/2" were unobtanium in Aust at an affordable price. Rob.
 
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