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
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Metric Oil Seals
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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The numbers on an oil seal, also known as a shaft seal or rotary seal, provide important information about its dimensions, material, and design specifications. Understanding these numbers is crucial when selecting the right oil seal for a specific application. Here's a breakdown of the typical numbering system used for oil seals:
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The first set of numbers usually represents the shaft diameter or the inner diameter (ID) of the oil seal. This measurement is critical because it indicates the size of the shaft around which the oil seal will be installed. For example, if the number is 25, it signifies that the oil seal is designed for a shaft with a 25-millimeter diameter.
The second set of numbers corresponds to the housing bore diameter or the outer diameter (OD) of the oil seal. This measurement is crucial as it indicates the size of the bore or cavity in the housing where the oil seal will be placed. For example, if the number is 40, it means the oil seal is designed to fit into a bore with a 40-millimeter diameter.
Rubber Skeleton Oil Seal
The third set of numbers or letter represents the width of the oil seal. It specifies the radial dimension of the seal, indicating how thick or wide the oil seal is. For example, if the number is 7, it means the oil seal has a width of 7 millimeters.
Some oil seals may have additional letters or codes indicating the lip type or special design features. These codes specify the sealing lip material, configuration, or any special features that the oil seal may have. Common lip types include single lip (S), double lip (D), and triple lip (T).
In certain numbering systems, a letter or code may be used to indicate the material composition of the oil seal. Different materials may be chosen based on factors like temperature resistance, chemical compatibility, and application requirements.
For example, if you have an oil seal with the number "25-40-7," it can be interpreted as follows:
Inner Diameter (ID): 25 millimeters
Outer Diameter (OD): 40 millimeters
Width: 7 millimeters
Understanding these numbers is crucial when replacing or specifying oil seals for machinery or equipment. It ensures compatibility with the shaft and housing dimensions and helps maintain effective sealing performance. When in doubt, it's recommended to refer to the manufacturer's documentation or consult with a supplier to ensure the correct oil seal is selected for the intended application.
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