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How to measure bearings

Measuring Bearings

How to measure and choose the correct bearing type

Reference Numbers

The quickest way to determine which bearing you require is using the bearings reference number.

Most bearings have their references numbers engraved on the bearings themselves, but these often rub off over time and so it may be necessary to measure the bearing yourself, as described below.

Measuring Bearings

It is sometimes necessary to measure bearings to determine the correct bearing type.

You can measure the dimensions of a bearing by using a vernier caliper like the one below or measuring accurately with a ruler.

All bearings will have a width, an inner diameter and an outside diameter.

Once you have determined the dimensions of your bearing, you can use our bearing search tool to find the correct bearing.

There are three main types of bearing – roller bearings, ball bearings and needle bearings. The differences between these bearings are detailed below.

Bearing Suffixes

Once you measured your bearing, you can use our search to find the correct bearing size.

e.g. Inside Diameter: 25mm; Outside Diameter: 52mm; Width: 15mm – Bearing Type: 6205

Once you know the bearing you need based on size, you can then choose further options:

The bearing also has a seal either side of the bearing and this will be indicated by the suffix:

ZZ or 2Z = 2 Metal Shields
2RS1 or 2RSR or DDU= 2 Rubber Seals

Additionally, bearings also have a clearance value. This provides the bearing room for expansion between the bearing races and will add a small amount of play between the two rings.

An example of where a larger clearance is required is if a bearing is likely to get hot. The heat needs room to escape otherwise there is a risk of bearing failure.

C2 = clearance is less than international standard
C3 = international standard for bearing clearance
C4 = clearance is greater than international standards

Bearing Types

Ball Bearing – A ball bearing uses loose balls to maintain separation between the two races.

Roller Bearing – The same as a ball bearing but instead of balls, a roller is used to maintain the separation, 

Needle Bearing – a small bearing which uses small rollers to reduce the friction between the races