SCD
Spring-loaded primary sealing lip with a springless secondary dust lip at the back of the seal. Used where material or fluid exclusion is needed in addition to fluid or liquid retention.
SCDC
Spring-loaded primary sealing lip with a springless secondary dust lip at the front of the seal. Used in space limited applications requiring a single function design.
SCDO
Springless double lip. Used when axial and radial space restrictions preclude the use of a SCDC seal.