Home >> Shaft Seals >> Oil Seals >> Glossary of Shaft Seal Terms


Bonded Seal:
Design feature of a type of radial lip seal. The heel of the sealing element is attached (Bonded) to the seal case by and adhesive during the molding operation.
Bore, Housing: (Bore, Seal)
A cylindrical surface which mates with the outside surface of the seal outer case.
Case, Inner: (Shell, Inner)
A rigid, cup-shaped component of a seal assembly, which is placed inside the outer seal case. It can function as: reinforcing member, shield, spring retainer, lip-clamping device.
Case, Outer: (Shell, Outer)
The outer, cup-shaped, rigid structure of the lip seal assembly. Acts as a protective cover for the head of the sealing element
Dynamic Seal:
A seal which has rotating, oscillating, or reciprocating motion acting upon it
An instrument which measures with an indentor point the hardness of rubber by penetration, without puncturing the surface of the rubber.
An elastic rubber like substance, such as natural or synthetic rubber
Feet Per Minute; used as a measure of shaft speed instead of R.P.M. To convert R.P.M into F.P.M., use formula .262 x R.P.M. x diameter (inches) = F.P.M.
Fluid Side:
Side of the seal which in normal use faces toward the fluid being sealed.
Garter Spring:
Coiled wire spring with its ends connected. It is used for maintaining a sealing force between the sealing element and a sealing surface.
Machine Lead:
Spiral grooves similar to a screw thread on a shaft surface that can result from improper finishing process; may result in early leakage.
Primary Lip:
The flexible elastomeric component of a lip seal, which contacts the rotating surface.
The average of all peaks and valleys from the mean line within cut-off (.010” of .254mm). Ra does not describe the surface profile (texture) and two shafts with the same Ra value can have very different surface characteristic.
Revolutions per minute.
The period of initial operation during which the seal-lip wear rate is greatest and the contact surface is developed.
That run-out to which the seal lip is subjected due to the outside diameter of the shaft not rotating in a true circle. Usually expressed as T.I.R. (Total Indicator Reading).
RZ (din):
Average peak to valley height
A type of wear in which is generally defined by the inside and outside lip surfaces and the spring groove
Seal, Heel Section:
The portion of the lip seal which is attached to the seal case.
Seal, Outside Diameter:
The external diameter of a lip seal assembly. Usually the outside diameter of the outer seal case.
Seal Width:
The over-all axial dimension of the lip-seal assembly. Normally the total width measurement of the outer seal case.
Sealing Element:
The normally flexible elastomeric component of a lip-seal assembly which rides against the shaft.
Secondary Lip:
A short, non-spring loaded lip, which is located at the outside seal face of a radial lip seal. Used to exclude contaminants.
Shaft Diameter:
The outside diameter of the shaft at the location where the seal is mounted.
Shaft Finish:
The relative roughness, usually expressed in micro inches, of the outside diameter of the shaft. The smaller the number, the smoother the finish.
Shaft Seal:
Generally considered to be a lip seal or an oil seal, but a broad definition could include and sealing device mounted on a shaft or sealing a shaft.
Sleeve, Wear:
A replaceable metal ring. Generally used in assemblies to eliminate expensive shaft replacement caused by grooving that may occur at the seal-shaft interface.
Shaft-to-Bore-Misalignment, the amount by which the shaft is off centre, with respect to the bore’s centre.


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