Leybold ISO-63K Retaining Ring for WS WSU WA WAU 150, 151,250, 251, 500, 501 Roots Blowers.
Leybold Part Number: ES23102401.
This is an Leybold ISO-63K retaining ring used on the intake on Leybold pump models WS WSU WA WAU 150, 151, 250, 251, 500, 501 Roots Blowers. Please see the second image for retaining ring location.