How to measure oil seals

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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