Who knows the answer?

[mattr]

Place i worked had some very rare and very specialist mixing equipment made by a company in Italy pre war.

Metric cartridge bearings. As in the actual balls. 10mm IIRC. Only reason they'd done it is they could choose the grade of material for bearings and races, and make sure only OE parts were fitted, which when they'd made the kit was important. By the time i was there (mid 90s) the bearings/balls were impossible to buy in any configuration. Loose, complete, custom. As the manufacturer had gone bust in the 40s.

So we remachined the whole lot to take stock cartridge bearings in the right grade of material (fairly standard stainless, almost unheard of in the 20s/30s).

 

[torqueless]

Re:

Perhaps because the universal adoption of the metric system is not that old compared to the history of the bicycle?

Perhaps SKF being the largest supplier of ball bearings even through WW1 and WW2 had something to do with it?

Case in point, I have a Swedish carpentry ruler from the 70s marked with three different inch measurements; London, Verktum, Norsk
plus Metric.

As they say, the good thing about standards is there are plenty to choose from.

Well, the fact that we are discussing this at all tends to suggest that the metric system has not been universally adopted? The OP is west of the Atlantic, which, perhaps bikes aside, is afaik a resolutely non metric place, in spite of, or maybe because of- being largely populated by refugees from Europe. France is famously metric, having established the system about the same time as the guillotine and the revolutionary calendar. I assume it is a French invention, later adopted by Germany and Italy, neither of which, iirc, existed as entities in 1790.

So was Sweden using inches in the first half of 20th century? Three different inches? I'd like to see that ruler!

Bikewise, I would imagine the demise of 'imperial' terminology in Britland went hand in hand with the demise of British componentry. If you've just traded GB, Chater Lea, etc. for Campag., Mafac, Stronglight, etc., I guess it no longer makes sense to be talking about 4 1/2" rear ends and such.. but even today, beyond bearing balls, there are holdouts.. frame sizes (at least colloquially if not within the 'industry'), 'TPI', etc.

The outside diameter of the ball has to match the radius of the cup or it will bind, the adjustability is available to take up the slack when the parts wear, they will still retain matching shapes albeit smaller so will need to be moved closer together (Or packed out with more grease )

Thanks t47b.. I don't want to give the impression that I'm in the habit of loading up races with approximately suitable balls, (although by some peoples standards I probably never do otherwise), but this is Retrobike, and I can't be the only one who has to deal with- or live with- decades-old bearing surfaces that might have been revolving around axles which for one reason or another might have developed less than perfect axial symmetry.. But the good thing about a bike is that it will still function under such circumstances, and only the rider will suffer. Take the same approach with an airliner and you are suddenly responsible for a couple of hundred involuntarily curtailed incarnations.

My understanding (someone correct me if I'm wrong) is that balls that are too large for their race will bind, and balls that are too small for their race will play. In the first instance the temptation is to slacken the adjustment, which introduces play, and in the second instance the temptation is to tighten the adjustment, which introduces bind.

 

[bigpantswheels]

Re:

We're a dumb lot here in the USA, couldn't figure out the metric system in the 70's, so we wen't back to what we knew ,sort of. Soda pop is still sold in 1 or 2 litre bottles but smaller sizes are still 12 or 16 ounces. Like I said were a dumb lot.

 

[sdp2112]

Re:

I have just noticed that in the 1958 Campa catalogue the ball bearings are specified in imperial sizes. It is the english version so perhaps they were being kind but it looks as if those of us the put 1/4 inch balls in our bb are safe.

 

[mattr]

You'll probably find that the reason ties very thoroughly into the industrial revolution in the UK. By the time the rest of the world had caught up the only place to get bearings or, more importantly, bearing making machines was the UK. Probably Birmingham.
Then you look at the patent thing. It's probably not worth the effort or expense. Just design your machine/product round imperial bearings.

Similar to things like tubing diameters and tyre sizes. A lot of the nominally metric sizes are actually conversions from imperial. As tooling for rims/tubes (extrusion dies and so on are not cheap)
You just have to look at how "successful" shimanos attempt at a 10mm pitch chain was.

Things like metric nuts and bolts are far easier than tubes, bearings, chains and so on as the tools are far far easier and cheaper to make.

Take the aerospace industry, the major suppliers and customers for fasteners are American, so all Rolls Royces drawings are in metric, except for anything related to nuts or bolts. So you end up with 144 holes on a 950mm PCD to take 3/16" 12 point nuts and bolts. Madness.