Loose ball bearing sizes. Imperial vs Metric

uart
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Loose ball bearing sizes. Imperial vs Metric

Postby uart » Fri Jul 13, 2018 10:23 pm

To the best of my knowledge most older bikes used imperial (inch) sized ball bearings, with the common sizes being 1/4", 3/16" and 5/32".

When I look to buy loose ball bearings on ebay however, I mostly see only metric sizes. Just wondering if modern bikes (or at least those that still use traditional cup and cone bearing) have changed over to metric?

Also, how critical is the sizing. Can 1/4" be replaced by 6mm, or 3/8" be replaced by 5mm. Just wondering.
Last edited by uart on Sat Jul 14, 2018 3:08 am, edited 1 time in total.

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Thoglette
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby Thoglette » Fri Jul 13, 2018 11:38 pm

Metric is different. You might get it to work but it'll not be happy.

Ball bearings are cheap. Buy the right ones. Getting cheap balls from ebay means you have no *****ing idea what you've buying - regardless of what the outside of the box says.

Plenty of decent imperial balls around in a variety of grades from reputable sources (e.g. Moruya Bicycles)
Last edited by Thoglette on Fri Jul 13, 2018 11:41 pm, edited 1 time in total.
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10speedsemiracer
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby 10speedsemiracer » Fri Jul 13, 2018 11:41 pm

uart wrote:To the best of my knowledge most older bikes used imperial (inch) sized ball bearings, with the common sizes being 1/4", 3/8" and 5/32".

When I look to buy loose ball bearings on ebay however, I mostly see only metric sizes. Just wondering if modern bikes (or at least those that still use traditional cup and cone bearing) have changed over to metric?

Also, how critical is the sizing. Can 1/4" be replaced by 6mm, or 3/8" be replaced by 5mm. Just wondering.


The metric ball is different to an imperial ball.
Eg; a 5/32 is 3.969mm/0.156in, whereas a 4mm ball is 0.157in. I've never swapped between. Maybe eBay isn't the answer in your case, and you may need to go into a bearing suppliers (is what I do) or an LBS. Not the cheapest but can't imagine it would be a big difference.
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10speedsemiracer
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby 10speedsemiracer » Fri Jul 13, 2018 11:43 pm

And just realised Thoglette has said what I said..sorry for the post congestion
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uart
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby uart » Sat Jul 14, 2018 1:53 am

10speedsemiracer wrote:The metric ball is different to an imperial ball.
Eg; a 5/32 is 3.969mm/0.156in, whereas a 4mm ball is 0.157in. I've never swapped between.


Yes I know. I've never interchanged them either. (BTW 5/32 is the only one that is truly close to the nearest mm size with a difference of only 0.03 mm, 3/16 and 1/4 are off by about 0.3 mm).

My key question is still unanswered though. Are bicycle cup and cone ball bearings still using imperial sizes, or is it only older bikes?

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P!N20
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby P!N20 » Sat Jul 14, 2018 11:16 am

I had the opposite experience when getting new ball bearings for my Campy hubs. Campy specifies ball bearings in metric to 1000th of a millimetre, but I could only find the corresponding sizes in imperial. From memory two sizes were bang on but the third was 1/1000th of a millimetre out. Hub still spins smooth.

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Re: Loose ball bearing sizes. Imperial vs Metric

Postby Torana68 » Sat Jul 14, 2018 11:54 am

.... and cheap arsed bearings may have a large size variation, avoid cheap eBay bearings unless they have the quality advertised ie ANSI/ABMA Standard 10A
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uart
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby uart » Sat Jul 14, 2018 1:27 pm

P!N20 wrote:I had the opposite experience when getting new ball bearings for my Campy hubs. Campy specifies ball bearings in metric to 1000th of a millimetre, but I could only find the corresponding sizes in imperial.

Ok. So you mean they specified the imperial sizes (like 1/4") but stated them in metric units like 6.350 mm. Well yeah, that's not really the "opposite" is it. It's actually exactly what I'm talking about.

I was just a bit miffed that when I enter "bicycle ball bearings" into the ebay search that I overwhelmingly got hits for sizes of 4mm, 5mm and 6mm in loose ball bearings (even when I specifically searched for BICYCLE ball bearings). Hence the question of "have they recently changed over" to these (whole number) metric sizes?

Anyway I've found a source of what appears to be good quality 1/4" and 3/16" from the US. So I will give those a try.

From memory two sizes were bang on but the third was 1/1000th of a millimetre out. Hub still spins smooth.

Which really leads to my other question about how much small size discrepancies actually matter. If you think about how a cup and cone works I think it should cope ok with small size discrepancies. I've never even considered replacing 1/4" (6.35mm) with 6.0mm for example, however I have seriously considered replacing 5/32" (3.969mm) with 4.0mm.

Remember that there are two types of discrepancies. One where all of the balls are the same size as each other, but all sightly different from the correct nominal size. And the other where the balls have poor size uniformity within the set. This latter type of variation is a bigger concern in my opinion.

Torana68 wrote:.... and cheap arsed bearings may have a large size variation, avoid cheap eBay bearings unless they have the quality advertised ie ANSI/ABMA Standard 10A

Yep thanks Torana68. That's the sort of size discrepancy that I want to avoid. :)

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Thoglette
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby Thoglette » Sat Jul 14, 2018 3:22 pm

uart wrote:My key question is still unanswered though. Are bicycle cup and cone ball bearings still using imperial sizes, or is it only older bikes?

Bikes with "modern" pretensions don't use cup and cone: they used sealed bearings (cartridges). I've personally never seen a cup-n-cone with anything other than imperial size bearings (but there's probably some French exception to prove the rule :D ).

Sheldon reminds me that "Most front hubs use 10 3/16" balls on each side; Most rear hubs use 9 1/4" balls on each side."

You can get Grade5 fairly easily these days - Grade 25 was the old "good" with 100 to 300 grades also being seen.
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Re: Loose ball bearing sizes. Imperial vs Metric

Postby uart » Sat Jul 14, 2018 3:52 pm

Thoglette wrote:I've personally never seen a cup-n-cone with anything other than imperial size bearings (but there's probably some French exception to prove the rule :D ).

Thanks Thoglette, that has also been my experience. Just wanted to know this for sure before ordering a load of them. :)

You can get Grade5 fairly easily these days - Grade 25 was the old "good" with 100 to 300 grades also being seen.


Yeah, grade 25 is what I'm looking at getting at the moment.

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Re: Loose ball bearing sizes. Imperial vs Metric

Postby P!N20 » Wed Jul 18, 2018 11:38 am

uart wrote:It's actually exactly what I'm talking about.


Good then.

So I checked my records, for my Chorus hubs Campy specifies the front bearings at 4.75mm, which doesn't quite equate to 3/16" which would be 4.7625mm.

The rear requires 6.35mm (NDS) which is bang on 1/4" and 5.55mm (DS) which isn't quite 7/32" which would be 5.5563.

As mentioned, hubs spin smooth despite the minor variance.

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Re: Loose ball bearing sizes. Imperial vs Metric

Postby uart » Wed Jul 18, 2018 1:11 pm

P!N20 wrote:So I checked my records, for my Chorus hubs Campy specifies the front bearings at 4.75mm, which doesn't quite equate to 3/16" which would be 4.7625mm.

The rear requires 6.35mm (NDS) which is bang on 1/4" and 5.55mm (DS) which isn't quite 7/32" which would be 5.5563.

As mentioned, hubs spin smooth despite the minor variance.


Thanks PIN, that's interesting. So they are still very close to the old imperial sizes, but rounded off to the nearest 0.05mm

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