How to measure oil seals

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

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 the most common are shown below,

R21 & 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,

To help you understand how the table works with imperial oil seal numbers here are a few example references,

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

(remember the first number is always the outside diameter)

137 62 25 = 5/8" inside 1.3/8" outside 1/4" wide

187 125 25 = 1.1/4" inside 1.7/8" outside 1/4" wide

150 250 37 = 1.1/2" inside 2.1/2" outside 3/8" wide

To identify the seals lip arrangement see previous table above.