There are some OEM’s that require the rubber O-ring for their water test requirements. 

Position one O-Ring over the nylon bushing and place it in the hole of the backplate,

The other O-Ring should be placed over the handle.

Buna O-Rings are used on the exterior and interior handles.

SEE DIAGRAM AND INSTRUCTIONS

Handle Bushing Color: Clear 

Buna O-rings: Black Rubber

Sold as 1 clear bushing and 2 black rubber O-rings