Leybold ISO-100K Retaining Ring for WS WSU WA WAU 1000, 1001 Roots Blowers.
Leybold Part Number: ES23102402.
This is an Leybold ISO-100K retaining ring used on the intake on Leybold pump models WS WSU WA WAU 1000 and 1001 Roots Blowers. Please see the second image for retaining ring location.