How to take your bearings in the markings on bearings, and not lose your mind?
The product range of bearings consists of many, many various items. A person seeing the markings for the first time might get the impression that they are some mysterious codes which can be understood only by erudite and experienced pundits. However, the truth is that after understanding the basic principles even a complete beginner can easily and promptly make sense of the system of the markings on bearings.
Unified identification rules them all (almost)
It is crucial for us that the general identification of bearings is governed by ISO standards, which are uniformly followed by all the producers in the whole world. Thanks to that there is no chaos in the identification. Therefore, when a European bearing producer makes a single row ball bearing, with 40 mm diameter of the inner circle, with 80 mm diameter of the outer circle and 18 mm of width, they will provide the bearing with the same identification marking as a producer from Asia or South America - that is with the code 6208.
Example of the significance of the markings
Let's see a concrete example of what we can read in the marking of a bearing. Let's use the aforementioned bearing 6208 to which we will add some further identification by way of example. Our exemplary item now bears the identification "6208 2Z C3".
First, we start with the basic identification 6208 and analyse it in detail:
- 6 — if the identification of a bearing starts with the number 6, it means that it will be a single row ball bearing
- 2 — will indicate the dimensional line of the bearing
- 08 — will precisely determine the dimension of the inner circle (shaft) which can be easily calculated as five times the value given (08 × 5 = 40 mm)
Now let's decode the additional marking 2Z C3:
- 2Z — means that the bearings have metal seals on both sides
- C3 — means a bigger radial inner clearance, or looseness, of the bearing
Now, the designation 6208 2Z C3, which at first sight does not tell us anything, suddenly informs us that we hold a classic single row ball bearing with the inner circle aperture of 40 mm, metal covered on both sides, with bigger radial inner clearance.
The system of bearing identification in detail
We already know that every standardized bearing has its basic number and additional designation. What type of information can the basic marking convey? Let's see again the bearing 6208.
We can learn three essential pieces of information from these four numbers:
- dimensional line
- diameter of the inner aperture of the bearing (the so-called hole)
The first numeral and the number of the digits in the basic marking jointly designate the type of bearing.
|First numeral||Number of digits||Type||Example|
|2||5||Spherical roller bearing||22218|
|3||4||Double-row angular contact ball bearing||3316|
|3||5||Tapered roller bearing||32207|
|4||4||Double-row ball bearing||4208|
|6||3 to 5||Single-row ball bearing||6208|
|7||4||Single-row angular contact ball bearing||7305|
The principle of identification of the bearing dimensional line is a bit more complicated. From the number following the bearing type we can identify the dimensional line. It specifies if a bearing is thinner and designed for a higher rotation rate and lesser load, or if it is more massive and can take bigger load but has a lesser acceptable rotation rate. The marking sequence goes from the thinnest to the most massive (7, 8, 9, 0, 1, 2, 3, 4). For instance: bearings 6708 and 6408 have the same diameter of the aperture of the inner circle. But the bearing 6708 is of the thin-wall type, whereas the 6408 type is massive and thick-walled.
The size of the inner circle
For the bearings with the inner circle aperture of 1 - 9 mm it can be easily determined by the last digit.
- 604 = 4 mm
- 636 = 6 mm
- 688 = 8 mm
It applies for the bearings with the inner circle aperture of 10 mm and larger that two last digits of the basic number determine the size of the inner circle aperture, according to these rules:
- 00 designates aperture of 10 mm, for example 6300
- 01 designates aperture of 12 mm, for example 6201
- 02 designates aperture of 15 mm, for example 6002
- 03 designates aperture of 17 mm, for example 6203
It applies for the bearings with the inner circle aperture of 20 - 480 mm that the aperture diameter is five times the last two digits, for instance, the aperture diameter of bearing 6212 is 5 × 12 i. e. 60 mm.
Additional bearing designation
Further modifications of bearings (for instance 2Z C3 from our example) are identified precisely by means of the additional designation. It can be put either BEFORE (prefix) or AFTER (suffix) the basic designation. The additional designation put BEFORE the basic designation is primarily used to determine if the bearing is made of stainless steel. (S with miniature bearings, for instance S 608 and SS or X with standard-sized bearing, for instance SS 6204). Therefore, the additional designation is mostly put AFTER the basic bearing designation.
Here is a rough overview of the most common additional designations:
- 2RS — Contact plastic seal on both sides of bearing, for instance 6208 2RS
- 2Z — Non-contact metal seal on both sides, for instance 6208 2Z
- N — Groove for security retaining rings on the outer circle, for instance 6208 N
- NR — Groove for security retaining rings on the outer circle already including the retaining rings, for instance 6207 NR
- C2 — Radial inner clearance lesser than the basic one, for instance 6208 C2
- C3 — Radial inner clearance bigger than the basic one, for instance 6208 C3
- C4 — Radial inner clearance bigger than C3, for instance 6208 C4
- C5 — Radial inner clearance bigger than C4, for instance 6208 C5
- K — Conical aperture in the inner circle, for instance 1207K
- M — Massive cage of bearing made of brass or bronze
- TNG — Cage of bearing made of polyamide
- V — Bearing with the full filling of rolling units, without cage
- P0 — Basic precision grade (usually this designation is not mentioned)
- P6 — Higher precision grade than the basic one, for instance 6207 P6
- P5 — Higher precision grade than P6, for instance 6208 P5
This article deals only with the basic explanation of the bearing identification, covering items governed by ISO standards. However, even in this fairly well-defined identification system there are numerous exceptions. Therefore, please do not consider this text exhaustive, but only as a basic introduction to this subject.
With a product range, where there are no ISO standards introduced, the situation is rather more complicated, since every producer uses their own identification. In that case, you can use converters, which we have developed for you to give you some assistance. If you are still at a loss or need a consultation, we are here for you. Please do not hesitate to call, write, or come in person and we will solve the issue together.
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