Leybold ISO-160K O-Ring for WS WSU WA WAU 2000, 2001 Roots Blowers.
Leybold Part Number: E23970512.
Leybold O-Ring,151.77 x 5.33 mm KFM (Viton), used for Leybold pump models WS WSU WA WAU 2000 and 2001 Roots blowers. Please see the second image for O-ring location.