Many ball bearings come in standard sizes. If the bearing you require is just an ordinary ‘standard type’, you can measure the size, (Bore x Outside Diameter x Width), or find the bearing size in a parts manual. With this information, you can easily buy an ‘off the shelf’ ball bearing.
As long as it’s not some weird and wonderful, specialised type of bearing, the information below is all you need to select and buy a bearing:
Make sure you measure the bearing in the correct format. Is it a metric or an imperial (inches) bearing? You can measure the bearing in either format, but in some cases, there may be a slight difference in size (dependant on the tolerances you’re working to?).
Use the following measurements, when finding the bearing size:
Bore (or hole diameter) x Outside Diameter x Width
or… Bore Ø x OD x W
This is where the bearing is open to the elements. It is therefore usually installed in a sealed protected environment or housing.
This is where the open bearing raceways are covered by a rubber seal to prevent the ingress of dirt and moisture.
These will have the abbreviation of: RS or 2RS
The rubber seal is generally thought to provide a better seal against ingress of dirt and moisture (compared to a steel seal).
This is where the open bearing raceways are covered by a steel crimped seal to prevent the ingress of dirt and moisture.
These will have the abbreviation of: ZZ or 2ZZ
Chromium Steel has increased wear and corrosion resistance over plain steel.
Stainless steel has increased wear and corrosion resistance over chromium steel (and are approximately twice the cost).
Ceramics are used in the manufacture of the ball bearings. They are much harder than steel and provide high wear resistance (and are approximately four times the cost).
The clearance (‘C’ rating) is the amount of play in the bearing. This sometimes needed due to heat expansion.
For precision (critical alignment) or where no great heat is generated, a ‘C’ rating is not required. E.g. a bicycle does not require a ‘C’ rated bearing.
The larger the number, the bigger the clearance: C3, C4, C5.
This isn’t always stated, but you may have a personal preference?
There are various types of bearings, and they come in a multitude of shapes and sizes. When you buy a bearing, sometimes it’s easier just to specify “I want a bearing for a widget machine” and the jobs done. But is it actually the easiest route to buying a bearing?
“Buying direct, cutting out the middle man will always be because of cost or the speed of supply”. I would guess that 99.9% of manufacturer’s buy-in their bearings.
Therefore, why not go directly to a bearing supplier (see the positives and negatives above)?