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Standard bicycle bearing ball sizes

Bicycles usually use ball bearings. Modern cartridge bearings come as a closed unit – with balls and races packed in a single unit. However, many bicycles still use older, cup and cone systems, where balls can (and should) be replaced with new ones when servicing bearings. This is the case with most Shimano hubs (wheels) – they still use the cup and cone system. This post lists standard ball sizes and gives guides on how to choose good quality ones, without the need to buy special, branded “bicycle bearing balls”.

Post explaining bicycle bearing types and construction: Types and designs of bicycle bearings.
Headset (fork bearings) standards explained: Bicycle headset bearings standards – SHIS.
Cup and cone bicycle hub overhaul tools and procedure: Bicycle hub overhaul.

Table Of Contents (T.O.C.):

  1. Quality (manufacturing precision) grades of bearing balls
  2. Bearing ball hardness
  3. Standard dimensions of bicycle bearing balls
  4. Conclusion
  5. Bearing ball dimension standards
    5.1. ABMA Std-10
    5.2. ISO 3290
    5.3. DIN 5401
    5.4. Ball size, grade and material table


1. Quality (manufacturing precision) grades of bearing balls

Grade defines tolerance (i.e. acceptable deviation) from a perfect sphere of a given diameter. Grades are noted in numbers, ranging from 3 to 2000. They are written in the format: GXXXX, where XXXX is a number ranging from 3 to 2000. The number represents how many millionths of an inch is the maximal deviation from the nominal dimension (with G1000 having a 1/1000″ deviation in sphericity, and G10 having a 1/100000″ deviation).

The lower the number after the G mark, the closer a ball is to a perfect sphere of a given dimension. Ball imperfections come in various terms:

  • surface roughness
  • waviness
  • egg shapedness (as a deviation from perfect sphericity)

For example, a ball of a grade G1000, with a nominal diameter of 6.35 mm (1/4″), can have a diameter varying from that size for over half of one-tenth of a millimetre. On the other hand, a G25 ball of the same nominal size will have a diameter more closely matching the nominal, with just a ±0.0013 mm maximal deviation. Similar goes for other types of deviations (surface roughness etc.). The lower the grade number, the closer a ball is to a perfect shape.

Since cups and cones in bicycle bearings have some elasticity and imperfections as well, balls of grade G25 are more than precisely enough machined (round and smooth). Going for higher grade balls (e.g. G10, G5 etc.) will not bring any performance, or durability benefits, just the balls will cost (needlessly) more.

– T.O.C. –


2. Bearing ball hardness

Bearing ball hardness is usually measured and expressed using the Rockwell HRC method. Values for hardened steel are usually in the range of 40 to 70. If a bearing ball is too soft, it will wear rather quickly, and then start damaging the cup and cone bearing because of increased play and imperfect alignment. On the other hand, if a bearing ball is too hard, instead of it getting worn, it will start wearing (softer) cups and cones of the bearing – that are more expensive and complicated to replace. That is why it is important for the balls to be of optimal hardness. The optimal hardness for bicycle ball bearings is between 55 and 65 HRC.

– T.O.C. –


3. Standard dimensions of bicycle bearing balls

Here’s a list of standard, most commonly used dimensions of bearing balls. There are other, exotic sizes, but they are extremely rare. To be on the safe side, when servicing bearings (and replacing balls then, which is always recommended), measure old balls. Best measured with a (Vernier) calliper.

Measuring, in this case a rear hub bearing ball, with digital calipers, showind dimension in inches
Measuring, in this case a rear hub bearing ball, with digital callipers, showing dimension in inches
  • 3.969 mm (5/32″) – steerer (fork) bearings and many pedals.
  • 4.762 mm (3/16″) – front wheel hubs (2 times 10 balls – i.e. 10 balls at each side most often).
  • 6.35 mm (1/4″) – rear wheel hubs (usually 2 times 9 balls) and cup and cone bottom brackets (2 times 11).
  • 5.556 mm (7/32″) Campagnolo Record front hubs and some exotic hubs of other manufacturers (2 times 9 balls).
  • 2.381 mm (3/32″) – most Shimano pedals bearing balls.

– T.O.C. –


4. Conclusion

It is good to replace bearing balls at each bearing service. They can be purchased rather cheaply (by 1000) from most hardware stores. Just make sure they are of proper grade (G25 or better) and hardness (HRC 55 to 65).

There is little point in going over the G25 grade, and absolutely no point going better than G10 (even that is an “overkill” for this application). Similarly, using balls softer than 55 HRC, or harder than 65 HRC can only decrease bearings’ lifespan.

Related post – Bicycle bearing grease:

What is the best bicycle bearing grease? Which type of grease to choose for bicycle bearings?
What is the best bicycle bearing grease? Which type of grease to choose for bicycle bearings?

Links for online ball bearing shopping from Amazon. As an Amazon Associate, I earn from qualifying purchases.

– T.O.C. –


5. Bearing ball dimension standards

Here are some charts showing bearing ball grades and dimension standards according to ABMA Std-10, ISO 3290, and DIN 5401:


5.1. ABMA Std-10

GradeSphericityDiameter
tolerance
per
lot
Diameter
tolerance
per
shipment
Surface
finish
GinchmminchmminchmmArithmetic
average
100.000010.00020.000020.0005±0.0001±0.002541
150.000010.00040.000030.0007±0.0001±0.002541
250.0000250.00060.000050.0013±0.0001±0.002542
500.000050.00130.00010.0025±0.0002±0.00503
1000.00010.00250.00020.0050±0.0005±0.01275
2000.00020.00510.00040.0102±0.0010±0.02548
3000.00030.00760.00060.0152±0.0015±0.0381n/a
5000.00050.01270.0010.025±0.002±0.050n/a
10000.00100.02540.0020.051±0.005±0.127n/a
2000n/an/a0.0050.127±0.005±0.127n/a
ABMA Std-10 bearing ball grades
Table 1

– T.O.C. –


5.2. ISO 3290

GradeSphericityVariation of
ball
diameter
Variation of
ball lot
diameter
Surface
finish
Gμ metresμ metresμ metresRa Max.
µ metres
30.080.080.13.010
50.130.130.25.014
100.250.250.5.020
160.40.40.8.025
200.50.51.032
240.60.61.2.040
280.70.71.4.050
40112.060
601.51.53.080
1002.52.55.100
2005510.150
ISO 3290 bearing ball grades
Table 2

– T.O.C. –


5.3. DIN 5401

GradeSphericityVariation of
ball
diameter
Variation of
ball lot
diameter
Surface
roughness
Gμ metresμ metresμ metresRa Max.
µ metres
30.080.080.13.010
50.130.130.25.014
100.250.250.5.020
160.40.40.8.025
200.50.51.032
280.70.71.4.040
40112.050
1002.52.55.060
2005510.080
5002525n/an/a
DIN 5401 bearing ball grades
Table 3

– T.O.C. –


5.4. Ball size, grade and material table

MaterialSmallest
standard
size
Largest
standard
size
Best
standard
grade
Lowest
standard
grade
Stainless SteelsmminchmminchGG
302/3041.51/1650.82501000
3161.51/1650.82501000
4201.51/1650.82251000
4301.51/1650.821001000
440c11/3250.82101000
CorrTech Steel11/3250.82101000
Other materialsmminchmminchGG
Chrome11/3250.8 2101000
Low Carbon11/3250.821001000
Brass1.51/1625.412001000
Tungsten Carbide1.51/1650.8210100
Borosilicate Glass23/3231.751.251001000
Soda Lime Glass23/3231.751.251001000
PlasticmminchmminchGG
Acetal (Delrin and Celcon)1.51/1625.41G0G3
Nylon1.51/1625.41G0G3
Polyethylene1.51/1625.41G0G3
Polypropylene1.51/1625.41G0G3
PTFE (Teflon)1.51/1625.41G0G3
Bearing ball sizes, grades, and materials
Table 4

– T.O.C. –

21 thoughts on “Standard bicycle bearing ball sizes”

  1. Thank you. Very helpful to know. Of course, this info might be found on internet somewhere, but i appreciate that you put such info together for readers’ convenience.

    Reply
  2. Having worked in a ball bearing plant for over 20 years. A grade 25 is round within 25 millionths of an inch, and within a given lot the ball to ball diameter variation is within 50 millionths of an inch. Likewise, a grade 10 is is round within 10 millionths of an inch and ball to ball diameter variation within a lot is 20 millionths. The convention is twice the roundness typically.

    Reply
    • I don’t know.
      If Google doesn’t help, suppose the only way is to measure the existing ones – if they are at hand.
      Maybe someone who knows will chime in.

  3. surface roughness
    wawiness
    egg shapeness
    thought I learned a new word today…wawiness

    Reply
  4. This is very helpful and you have solved my problem of what size my bearings are so I can buy replacements.
    Thank you. Stuart

    Reply
  5. This is a good piece of information. Thank you for sharing. I have French pedals from the 1940s, with ball bearings that I measure as 3.15mm. Everything else on that bike is non-standard, (thread pitch, bottom bracket, stem diameter, post diameter,….). Maybe the pedal bearings were uncommon too. I am still searching for new ones of the correct size.

    Reply
    • 3.15mm as measured is likely just to be standard 1/8″ balls, I would have thought…

  6. I recently purchased a 26inch Beinaiqi cavalier fat bike, my question is, can I put cartridge bearings in my rear hub or should I stay with the cup & cone system ?

    Reply
    • I don’t know how one would put cartridge bearings into a hub with cup and cone bearings (or vice-versa for that matter).
      The usual way of achieving that is getting a different hub.

      But I wouldn’t sweat it too much – cup and cone bearings are relatively easy to service and can last a long time if serviced regularly (generally: once a year, or each 5000 km, whichever comes first).

  7. in australia alot of people just throw old bikes into the street when they cant be bothered to fix them,i totaly strip older bikes for parts and sometimes i even find a nice spare bike to fix up,i re-use bearings,cassettes handle bars you name it,i even find new tubes and tires that are thrown away.

    Reply
  8. Great explanation, thank you!
    This article just saved me a lot of time, I overhauled the wheels of 3 bikes at the same time last week , and today
    I found a ball stuck to my shoes, ~6.3mm in diameter. Where does it belong? It’s not from my old Peugeot, they use thin hubs and smaller balls. Not from the front of Raleigh, that should be 3/16″ (~4.8mm), so it should be from the rear of Raleigh! Just one wheel to open and insert the wheel, a 10 minutes job! In my defense, the bearing on the cassette side looks smaller, at the time it seemed logic to have 8 balls instead of 9.

    Reply
  9. Thanks for the advice on loose bearings, the bearings in my Shimano hubs are held in a cage, can I just put new bearings in the old cage? If I can source non Shimano bearings in a cage is it enough to just match the dimensions of the cage or do they come with different profiles to fit into the hub races?
    Thanks.

    Reply
    • Hi Andy,

      I suppose you could use the old cages with new balls.
      However, I prefer tossing the cages out and putting more loose bearing balls (more will fit once the cage is out).

      An exception to that are hubs that have a huge amount of bearing balls that are too fiddly to fit one by one.

      Relja

  10. cages are only made to make it easier to install bearings,they serve no other purpose,bearings run alot better without cages,those cages allways cause problems,fine bearings in cages around steering stem i only use as those bearings are just to fine to install whithout a cage.when using loose bearings leave a space,you fill the whole space with bearings then you remove one or two bearings so there is a space,if you dont leave a space between those bearings they will grind away and not run smoothly

    Reply
    • Hi Lukasz,

      Thank you very much for the correction. If you notice any other mistakes, don’t hesitate to not them. It’s appreciated. 🙂

      Relja

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