How to measure a bearing
Sometimes you may need to identify a bearing due to general wear and tear. Most bearing references now are laser stamped but these wear and rub off more quickly than the previous method, which was engraved deep in the bearing's metal.
Each bearing has an inside diameter, outside diameter and width diameter in that order. Most bearings are metric in size, but can also be imperial or a combination of both.
d = Inside diameter
D = Outside diameter
B/T = Width diameter
You can search for the size 25x47x12 or the bearing name 6005-2RS or you can look in our bearing lists. Once you have identified the bearing's size some bearings come complete with seals and with more or less clearance than normal.
Example of bearing 6005 size (See picture above)
d = 25mm
D = 47mm
B/T = 12mm
There are also a lot of different kind of seals or have a greater clearance than normal bearings.
RS = Plastic seal on one side.
2RS = Plastic seal both sides.
2RSH = Plastic seal both sides.
2RU = Plastic seal on both sides.
DDU = Plastic seal both sides.
2RSL = Low friction seal / grease (high speed).
2RZ = Low friction seal / grease (high speed).
LLU = Sealed both sides.
ZZ = Metal seal both sides.
2Z = Metal seal both sides.
C3 = Greater clearance in cold bearing.
C4 = Greater clearance in cold bearing.
NR = for retaining ring
Example of different types
The internal clearance being C3 means that the bearing has room for expansion if needed between the races of the bearing, whilst holding the outer ring and moving the inner ring in a radial movement you will detect a little amount of play between the 2 rings. All standard clearance bearings have this movement, it may only be a small amount of movement but is controlled by international standards. C3 means the bearing has more clearance than standard and C4 means the bearing has more clearance than C3.
For example, you may use C3 or C4 clearance on bearings in engines with high revs and/or with high working temperatures and these bearings will make the engine run “easier” and makes more power. However, an engine with C3 and C4 bearings needs to warm up a cold engine on low revs until it’s up to normal working temperature or the greater clearance may cause a bearing failure.
C2 = Clearance less than normal
C3 = Clearance greater than normal
C4 = Clearance greater than C3