O-ring 7173016 ( 1.109 I.D. x 1.387 O.D.) - sold individually,,
Or in Pack of FOUR ( 4 ) as Required for use inside the Larger version 1" By Pass Valve 7214383, WS15X10026.
These go on the by pass stem ( sliding shaft ).
If you want 4, then be sure to select quantity of 4