2-piece Inner Wheel Seal (Rolling Diaphragm Seal) used on late ~5/95~96 1/2-ton 4WDs.
The pair is MotorCraft
BRS23 or F5TZ-1S190-AA. The original-design rubber seal is
MotorCraft BRS78; the revised rubber seal is
BRS86; the steel seal is
MotorCraft BRS85#6&7 in this diagram:
ERROR: It was NOT used on '93-94s, and can't be used on them without changing the spindle AND hub.
The black seal slips onto the spindle. The side visible in this pic goes OUTboard against the smooth surface of the metal seal; the smaller ring slips over the spindle's base shoulder. APPLY GREASE to the larger lip or the wheel will squeak. Either wheel bearing grease, or silicone grease (preferred), or PTFE (teflon).
See also: