Since when did 3/8" = 9.2mm?

Fordman

1000+ Posts
Apparently a 3/8" bolt is now a 9.2mm bolt, according to Zenith Hardware!
Yes it measures 3/8" dia.

IMG_20210507_125708076_red.jpg
 

Whippet

Member
Hi Fordman.

This sort of stuff drives me nuts, pardon the pun. If fastener manufacturers' want to go all metric, then why don't they simply use M10 instead of persevering with 3/8" UNC; and similarly across the other size ranges.
 

seasink

1000+ Posts
Is it not illegal to advertise products in imperial units? I know a ban cause much grief in the construction industry in the 70s. At one point sale of foot and inch tapes and rules were banned. Metrication was forced on a largely unsympathetic public who were at home with the old system..

You either got labels like this one or "nominal 10mm".

Since pipes, unlike bolts, have never changed size, they are now described as nominal bore and a rounded mm size.
 

JohnW

Too many posts!
If I recall, when we went metric in about 1970-1, for some time it was indeed illegal to advertise in Imperial units and tape measures had to be metric etc. I think that was relaxed later.

What just boggles my mind is that a full 50 years later we still go to shops and can't find metric fittings. I was looking for metric fibre washers in Supercheap and they only had Imperial. It must be some old manufacturing plants in Oz still supplying the cheap end of the market I suppose.

Our Renaults with Lockheed brakes all have non-metric threads on hoses and fittings, so we can get hoses made just down the road, so there's one thing good about this I suppose. Pipe and tubing threads are another matter. I vaguely recall that BSP threads, the big ones over 3/4" or something like that, are Whitworth with a slight taper and the small GAS threads are non-metric too.

Just count your blessings that you didn't work in the drilling industry, putting 6 5/8" holes down to 250 m and working out cement volumes. All API standards in inches and things.
 

59 Floride

Member
We recently had a client who was buying an apartment off the plan and he requested we do him a set of drawings in imperial measurements so he could relate better. To convert a full working set of 450ish drawings from metric to imperial for one client was a big ask. Request denied .
Yes Kids it's been 50 years, get with it.
 

bluey504

1000+ Posts
Zenith must have 'finally' got the message....still won't do M4 nuts and bolts as they see, or hear, no need for them....except for drawer handles that other manufacturers do!
:drink:Brendan.
 

JohnW

Too many posts!
We recently had a client who was buying an apartment off the plan and he requested we do him a set of drawings in imperial measurements so he could relate better. To convert a full working set of 450ish drawings from metric to imperial for one client was a big ask. Request denied .
Yes Kids it's been 50 years, get with it.
I can only think of printing the plans at a scale that works and post him an old scale rule. I used to do engineering geology mapping at 40 feet to the inch as a student.
 

seasink

1000+ Posts
Why didn't you print the drawings to 1:96 or 1:48 or 1:24 and send along a suitable scale?

I remember the changeover, and it slowed everything down mightily and made more than a few design jobs lose money. Every draughtsman had conversion tables and metric brick rods taped all over his board. I also remember how slowly people who had worked all their lives in the old units worked when converting. Not only with foot/inch but also the SI units Pascals, Newtons etc. In those days calculators were a very expensive new thing, and the the primitive desktop computers were not to be found in design offices.

There was a period allowed for changing, and some very large jobs deliberately did not change. I was in charge of one. The decision (not mine) was based on getting the job done with fewer man-hours. It was constructed in old units well into the metric era.
 

Kenfuego

1000+ Posts
As I have previously posted, just after we went Metric in Australia, the ethnic European tradesmen who were then working on our house, pointed out that ours was not a true Metric system, it was largely symbolic with common imperial sizes of manufactured goods used in construction simply still being used but given a "metric equivalence"

Ken
 
For the last 10 years of his career my father valued the Melbourne city skyscrapers using the imperial measures he has used all his life and converted to metric only at the very end of the calculations.

Roger
 

JohnW

Too many posts!
For the last 10 years of his career my father valued the Melbourne city skyscrapers using the imperial measures he has used all his life and converted to metric only at the very end of the calculations.

Roger
I can quite understand that! Probably the best approach for him at the time.
 

seasink

1000+ Posts
We didn't always hard convert Ken, with a few troublesome exceptions. It would have been disastrous if nothing fitted anymore. The Europeans did not hard convert many things either, and your tradesmens' comments weren't really justified

We adopted the SI system, which was not used in Europe.

There was a call by very loud voices for hard conversion, but practicality prevailed. Tiles are the obvious building component to actually change, though metric sizes in new things like universal steel sections have occurred. Timber sizes are before sawing or dressing and whether you say 4x2 or 100x50 is not important - both are nominal

In Europe nominal metric dimensions abound for things that never changed. BS in a metric disguise still applies to European pipework for example. A 2 inch pipe is not exactly that in diameter, and a Euro 50 mm one isn't either. Both are nominal.

Bricks vary by country or even region, but have remained trad sized. If you look at French or German detailed drawings you will see odd metric dimensions that are disguised traditional. like multiples of 25.4.

Europeans didn't make our troffer light fitting mistake. In a drive to make everything metric modular, ceiling tiles and their framing shrank from 1 foot to 300 mm. However the international (including Euro) standard for fluorescent tubes remained at 4 feet over all. The troffers had to redesigned with an overhang, and can no longer be butted.

Metric modular clay bricks were used quite a bit in the 70s. You don't see them much now. Their main benefit is visual.
 

JohnW

Too many posts!
We didn't always hard convert Ken, with a few troublesome exceptions. It would have been disastrous if nothing fitted anymore. The Europeans did not hard convert many things either, and your tradesmens' comments weren't really justified

We adopted the SI system, which was not used in Europe.

There was a call by very loud voices for hard conversion, but practicality prevailed. Tiles are the obvious building component to actually change, though metric sizes in new things like universal steel sections have occurred. Timber sizes are before sawing or dressing and whether you say 4x2 or 100x50 is not important - both are nominal

In Europe nominal metric dimensions abound for things that never changed. BS in a metric disguise still applies to European pipework for example. A 2 inch pipe is not exactly that in diameter, and a Euro 50 mm one isn't either. Both are nominal.

Bricks vary by country or even region, but have remained trad sized. If you look at French or German detailed drawings you will see odd metric dimensions that are disguised traditional. like multiples of 25.4.

Europeans didn't make our troffer light fitting mistake. In a drive to make everything metric modular, ceiling tiles and their framing shrank from 1 foot to 300 mm. However the international (including Euro) standard for fluorescent tubes remained at 4 feet over all. The troffers had to redesigned with an overhang, and can no longer be butted.

Metric modular clay bricks were used quite a bit in the 70s. You don't see them much now. Their main benefit is visual.
Interesting. That set of things is why our deck wall is set back 2400 mm from the parapet wall. It's 8 feet of course.... SI units are a hard master in a way - the cm is a useful unit but not SI, so we have mm and m........
 

seasink

1000+ Posts
2400 mm, ie nominal 8 feet, is on the recommended 300 mm module. When plasterboard and other sheets went modular, ceiling heights came down approx 1 1/2 inch.

Door sizes are based on nominal wall openings, so haven't really changed. A standard door is 2040 high, a whisker off 80 inches or 6'8". They are still 1 3/8" thick, sorry 35 mm.
 
Last edited:

Kim Luck

1000+ Posts
Wire rope is still sold in both Imperial and Metric sizes. We need to understand that the USA is the reason we still have two different systems. The rigging on an Etchells yacht designed in the USA and raced worldwide is specified in Imperial units. Woe betide any owner silly enough to turn up with any form of Metric equivalent. For instance, the Etchells wire backstay must be 1/8" dia. not 3mm.
 
Top