Specs that are part English and part metric

I seem to remember that some European bicycle parts had similarly stupid threads...

Paul

Shaft nuts---the thin round nuts with notches in the rim used to retain bearings on shafts. Metric diameter, English pitch.

There's a lot of specialty farm equipment where english nut and bolt wrench sizes were speced. Not the bore and thread, so they are metric if that component was built on the far side of the pond. Not a problem till you lose a bolt or nut. Fastenal thought I was nuts, even they hadn't seen that.

My JD5310N has some of this, some pure metric, and some pure english. All the fastener lengths are non standard. At least you can order replacement fasteners from JD, just hold on to your shorts when you see the bill.

Karl

Tyre Sizes are mostly given (cast into the rubber) With the wheel diameter in inches and the tread width in millimetres.

John G.

Campagnolo bicycle axles. 9 and 10mm x 26tpi.

There was the unfortunate era of "soft metric" where the diminsions of an "inch" part were simply converted to 3-place metric and called metric.

Lead to all sorts of ugly roundoff errors for the designer that allowed the tolerance to build up.

Although not quite the same, US aviation uses a very strange hodgepodge mix of units..

Statute miles for visability Nautical miles for navigation Degrees Celsius for temperature Inches of mercury for atmospheric pressure Knots for horizontal speed Feet per minute for vertical speed

IIRC the thread was Cycle Engineering Instutute (CEI)

Set the lathe for 26 tpi and make whatever you needed.

Not as bad as the BA series of threads, where the sizes and pitches are nominally english, but based on metric measurments.

Cheers Trevor Jones

British Standard Cycle thread = BSC = 26tpi

I could send you about 5# of 1-1/2 inch long HHCS in 1/4-20 thread with

And they ain't bad 6mm X 1.0s either. They're real honest-to-God 1/4-20.

God alone knows where those came from. I've never seen them as original parts on any of the wheelchairs come into our shop. Been some chairs go out with them though. :)

I have some similar to those . I think the thread must have been spect. by the US Co. but the heads wernt so the Asian mfgr. used metric for the benefit of the assemblers who have metric tools. Or something like that. ...lew...

Knots and nautical miles are based on degrees of longitude and latitude and the size of the Earth. The Metric system was intended to make the Earth's circumference come out to an even 40,000 Kilometers but the surveyors made (and then covered up) mistakes.

jw

============ I was told that this resulted from the "Marshal Plan" where many surplus US [inch] machine tools were shipped to Europe after WW2.

While transposing gears are a possibility, you can no longer use the half-nut, so there is a significant production penalty to generate metric threads with an inch lead screw.

Thus the "compromise" where diameters, lengths etc. were metric and the threads the closest possible inch equivalent, i.e. 26 tpi close to 1.0 mm pitch [25.4 tpi]

No documentation, but sounded plausible.

Unka' George [George McDuffee] ============ Merchants have no country. The mere spot they stand on does not constitute so strong an attachment as that from which they draw their gains.

Thomas Jefferson (1743-1826), U.S. president. Letter, 17 March 1814.

Car tyres have metric width and imperial rim diameter. Except some (rare) American(!) rims, which have metric diameter.

I have heard that the Italian model engine manufacturer Super Tigre used to use bearings with metric outside diameter and imperial inside diameter. I have never seen a bearing like that myself, though, so I can't vouch for the accuracy of this.

Computer monitor size is measured in inches, while the pixel resolution (dot pitch) is measured in millimeters.

My US-made ATK had a ball bearing in the swing arm that had an imperial OD and a metric ID (or the other way round?). I fell off the bearing dealer's chair when I went there (had no time to measure, so I took it there directly; needed it anyhow) and he lifted his eye-browns more and more the more he measured. That was a Tuesday. Friday night off for a race. No chance to get that bearing! Made some kind of funny boring bar that was driven by a hand drill and berserked two bigger holes into the (**very** nicely TIG-welded!!!) frame and made a new axle and bushings.

BTW, the bb's were made in China. Completely disintegrated in the middle of the season.

"ATK: Crafted with pride in the USA." LOL!

Nick

LOL! Marshall, not Marshal. And the flow of tools was quite the other direction.

At that time, everyone no longer thought about making imperial threads. That "confusion" has ended decades before. At least in Germany.

Nick

I've seen socket cap screws the other way 'round - metric threads with fractional hex sockets. If you order a Huco Oldham coupling (made in Engalnd) with a fractional inch bore it comes with them. Order a metric bore and you get regular all metric screws.

Interesting.

I had no idea the practice might be so common.

Thanks, All.

There some small watch screws that use this system, metric diameter and the threads per inch.