How Do You Measure Oil Seals?

Please note that under most circumstances, you will not need to measure the oil seal itself. To size the seal correctly, you just need to know the shaft diameter, bore diameter, and bore depth of the equipment that you took the seal out of.  

One situation in which you might need to measure the seal itself however, is if you are trying to verify its manufactured size. The most important dimensions on an oil seal are the ID (inner diameter), OD (outer diameter), and width. We do not recommend trying to measure the ID of the seal, as it is very difficult to do without stretching or altering the lip. The OD of the seal can be measured most accurately with a special piece of equipment called a pi tape. The pi tape is able to take into account any out-of-round condition with the seal that a pair of calipers might not. The width of the seal can be measured with a pair of calipers, taking a few measurements around the whole diameter.