Metric Oil seals will usually have the sizes written on it, for example 20 40 10 written on the seal tells us it will be a 20mm Inside Diameter (ID) a 40mm Outside Diameter (OD) and 10mm Wide/Thick.
If nothing is printed on the seal you would just need to take Vernier etc and measure the ID,OD and Width.
You may also see letters on the seal, if it has TC this means it is a Double Lip (R23) seal or if SC is written on it this means a Single Lip (R21)
Buy Oil Seals Now!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
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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