Replacing a critical component can be difficult to get right, especially if you do not have the original machine specifications. Thankfully, there are a few ways to identify oil seals; from their design, size and material. As there are hundreds of different oil seals available on the market, this guide will cover the four most common design types. Typically available with either a single or double lip, in Nitrile or Viton Rubber Material.
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Firstly, the oil seals covered in this guide classify the single lip as the inner diameter at the bottom of the component. The single lip is vital to the function of the seal by containing the oil, grease or lubricant. The only difference between a single and double lip is the additional rubber lip on the top of the oil seal which helps prevent dust or dirt from coming close to the shaft. Identifying the oil seal lip can be misinterpreted with a visual inspection alone. For or this reason, you should press along the inner diameter at the top of the seal, if you feel a ridge with a slight movement or give it is highly likely you have a double lipped oil seal.
Industry retailers use unique codes to identify oil seals worldwide. The most common lip style designations are 21 (single lip) and 23 (double lip), please read our Oil Seal Cross Reference Guide for more detailed information.
Fully covered outer diameter for excellent sealing. This oil seal is fully enclosed in a rubber material and is the most widely used type of oil seal. Great resistance to thermal cycling, temperatures and different chemical resistance.
Economic metal outer diameter for standard applications. This is an economical oil seal where the metal is exposed on one side and offers a closer fitting between the oil seal and housing or bore. Due to this, it has limited use with sealing thin liquids or gases.
The same design as type B with an additional inner case for greater structural rigidity. This type of oil seal is typically used in heavy-duty engineering machinery or large diameter sized seals
The same design as type A with corrosion protected metal case and stainless-steel garter spring. Suitable for use with a wide range of fuels and chemicals.
Nitrile or NBR is black in colour, whereas, Viton or FKM is usually a brownish colour. To understand the main comparisons between the two compounds read our Nitrile vs. Viton article.
Finally, Polymax part codes follow the same pattern as our O-rings - inner diameter, outer diameter and height. This is different from the industry-standard convention, whereby imperial oil seals follow - outer diameter, inner diameter and height.
We hope the information in this article helps you identify the correct oil seal for your application. If you have any queries feel free to call one of our sales engineers on 01420 482862. Polymax stock over 6,000 oil seals available to buy online, browse our oil seal selection today.
Identifying oil seals can be tricky especially the imperial sizes so here is a little guide that will help you get your job up & running again quickly
Metric Oil Seals
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Metric oil seals are more or less straight forward as the size is stamped on the seal for example 20 47 7 this indicates that the inside is 20mm, outside 47mm & width 7mm, some oil seals have different lip arrangements
SC=R21 & TC=R23 being the most common R21=Single Lip R23=Double Lip
So for example if you had on your oil seal TC 20 47 7 you would now know that you would need a double lip seal with a 20mm inside, 47mm outside & 7mm width.
Imperial Oil Seals
imperial oil seals are a little more tricky as the numbers on the oil seal are not in fractions & they always start with the outside diameter first for example 300 212 37 this indicates that the oil seals sizes are 2.1/8" inside, 3" outside & 3/8 wide, below is a table to help you convert these numbers,
1/16 0.06
1/8 0.12
3/16 0.18
1/4 0.25
5/16 0.31
3/8 0.37
7/16 0.43
1/2 0.50
9/16 0.56
5/8 0.62
11/16 0.68
3/4 0.75
13/16 0.81
7/8 0.87
15/16 0.93
1 1.00
To help you understand how the table works with imperial oil seal numbers here are a few example references,
(remember the first number is always the outside diameter)
137 62 25 = 5/8" inside x 1.3/8" outside x 1/4" wide
187 125 25 = 1.1/4" inside x 1.7/8" outside x 1/4" wide
150 250 37 = 1.1/2" x inside 2.1/2" x outside 3/8" wide
To identify the seals lip arrangement see previous table above,
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