Hub Outer Dial O-Ring. There is a small rubber O-ring located between the inner and outer hub dials. If this ring becomes damaged water and dust can leak into the hubs.

It can also make turning the dial difficult. Easy to install using snap ring pliers and 10.0 mm socket. OEM replacement.
Specs:

• Warranty: 12 Month Limited Warranty
• Sold As: Each
• Material: Rubber
• Finish: Bare
• Color: Black
• Fits: 1979-1995 Toyota Pickup, 1985-1995 Toyota 4Runner