Radial shaft seals are used between rotating and stationary machine components or between two components in relative motion and consist of two main parts:
A cylindrical outer covering of sheet steel （case） or elastomers that have the requisite interference fit to seal statically against the housing bore.
A sealing lip made of an elastomeric or thermoplastic material that seals dynamically and statically against the shaft.
The lip has a sealing edge that is formed by molding, cutting or grinding.
It is normally pressed against the counter face surface of the shaft, with a defined radial load, by a garter spring.
The edge of the sealing lip and the shaft counter face surface form the most important functional area of a radial shaft seal. The sealing effect of the lip can be enhanced by designing the contact area of the lip with hydrodynamic features.