They had to go and make things difficult I guess back when I bought more seals they had the size marked right on them if they were metric oil seals they were 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 seemed to be R21 and SC for single lip, and R23 and TC for double sealโฆ of course there were many moreโฆ other numbers or letters would indicate the type of material the seal was made fromโฆ
With imperial sizes it was somewhat more complicatedโฆ I believe the first number is always the inside diameter and an example would be,
150 250 37 or 15025037TC = 1.1/2 inside 2.1/2 outside and 3/8" wide double lip sealโฆ
There were conversion charts to make it easier that went something like thisโฆ
1/16= 0.06
1/8= 0.12
3/16 =0.18
ยผ= 0.25
5/16= 0.31
3/8= 0.37
7/16 =0.43
ยฝ= 0.50
9/16= 0.56
5/8= 0.62
11/16= 0.68
ยพ= 0.75
13/16= 0.81
7/8= 0.87
15/16= 0.93
1= 1.00
I guess that has all changedโฆ
Double lip seals do a better job for their intended purpose, they are better where they are needed but not necessarily better for all applicationsโฆ there are different styles of single and/or double lip seals that combined into many different configurationsโฆ For the most part one lip is designed to keep contaminants out and the other to seal the lubricant inโฆ double seals produce more friction and heat and deteriorate more quicklyโฆ
Love my mass produced, entry level, built by Lazy American Workers, Hornet