How to Measure Oil Seals: Shaft (ID), Bore (OD), and Width (THK)

How to Accurately Measure Oil Seal Dimensions: ID × OD × Width

Engineering standards always list oil seal dimensions in the sequence: d × D × B (Shaft Diameter × Housing Bore × Seal Width).

1. Measure Inside Diameter / Shaft (d): Use the outside jaws of a vernier caliper to measure the machine shaft where the seal operates. Do not measure the soft lip of an old, worn seal as it will be distorted or undersized.
2. Measure Outside Diameter / Housing Bore (D): Measure the internal diameter of the housing bore where the outer case of the seal press-fits.
3. Measure Thickness / Width (THK / B): Measure the axial depth/thickness of the seal body.

Precautions When Converting Inch to Metric Specifications

If you cannot find an imperial (inch) replacement and need to substitute with a metric size, pay extreme attention to housing bore fit (OD). Even a fraction of a millimeter difference can lead to a loose press-fit, causing the seal to back out under operating pressure or leak around the outer casing.