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.

How to measure bearingswith a protractor

This is where the bearing is open to the elements. It is therefore usually installed in a sealed protected environment or housing.

This isn’t always stated, (and you may have a personal preference?). But it’s always worth trying to determine whether oil or grease was used as the original lubrication in the bearing when new.

How to measure bearingsMaths

How to measure bearingsGCSE Maths

“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 that use bearings, buy-in their stock.

As long as it’s not some weird and wonderful, specialised type, the information below is all you need to select and buy a bearing:

There are various types, 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?

Therefore, why not go directly to a bearing wholesaler (see the positives and negatives above), rather than to an original equipment supplier (who buys in their bearings)?

Bearing size calculator

How to measure bearingswith a ruler

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The basic requirement is to replace the bearing with the same type. Going by the names, you can generally select the correct type:

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).

Bearings will often contain a seal to prevent the loss of lubricant and to prevent the ingress of dirt and debris. There are generally, two types of seal:

How to measure bearingson a map

Make sure you measure the bearing in the correct format. Is it a metric or an imperial (inches) bearing? You can measure in either format, but in some cases, there may be a slight difference in size (dependant on the tolerances you’re working to?).

The rubber seal is generally thought to provide a better seal against ingress of dirt and moisture (compared to a steel seal).

Many ball bearings come in standard sizes. If the item you require is just an ordinary ‘standard type’, you can measure the size, (Bore x Outside Diameter x Width), or find the size in a parts manual. With this information, you can easily buy an ‘off the shelf’ ball bearing to replace one that’s worn out.