bearing sizes

[pcatterall]

Apologies for starting a new thread as my last thread did not separately address the question.

We need to replace the bearings in my wheel pilot. The old ones measure 7.9mm ( with my cheap digital calliper)
I would have thought that Raymarine products would be metric and assumed that I need 8mm bearings.
I was advised that 7.9mm is nearer to 5/16ths" than 8mm.
Should bearings called 8mm actually measure 8mm or are they made slightly smaller to 'occupy' an 8mm space in
a race.

In other words... is there a specialist on board who can improve our general knowledge about bearing sizes??

 

[Jaguar 25]

Assuming that you are talking about ball bearings, most, if not all, have a code engraved onto the side wall that defines exactly the bearing including size.

 

[RIBW]

... is there a specialist on board who can improve our general knowledge about bearing sizes??

I usually receive good support from Simply Bearings on both bearings and seals. They have a useful selection tool on their website. E.g.:-

https://simplybearings.co.uk/shop/a...keywords1=8&keywords2=Outside&keywords3=Width

They sell in small quantities, provide online specifications and prices & delivery are good.

Cheers
Bob

 

[RobinBirch]

Another good outfit that you can speak to and get advice etc https://www.bearingboys.co.uk/

 

[ean_p]

lookie here...!

http://www.engineerstudent.co.uk/bearing_numbers_explained.html

 

[earlybird]

Should bearings called 8mm actually measure 8mm or are they made slightly smaller to 'occupy' an 8mm space in

Balls from a bearing supplier will be extremely close to their nominal size. Much closer than you can determine without high quality measuring equipment. Incidentally, Google brings up an Amazon listing of 7.9mm balls, but as these are from an American bicycle shop, I wouldn't be surprised if they were actually 5/16".
I suggest you beg/ borrow/steal a decent micrometer, which is rather better than a cheap vernier, measure what you've got and purchase a complete set of balls to the nearest size to fill your pilot. They're not expensive, and best not to mix sizes if you're not certain.

 

[pcatterall]

Thanks all. I have had good info from 'bearing Boys' in the past.
I should have made it clear that it is the actual ball size I am referring to.
For this exercise I have gone ahead and ordered them as 5/16" I will check the 10 in line against the originals.