These Leybold ISO-100 intake collar rings are designed to bolt-down an ISO-100K flanged fitting to the intake of a WA-1001, WAU-1001, WS-1001, or WSU-1001 model Roots blower vacuum pumps. The ISO-100K flange is typically used with double claw clamps. However, these bolt down collar rings and required snap ring that fits into a groove on the outside edge of the ISO-K flange allowing the bolt down collar to fasten the ISO-K fitting to the intake for the Roots blower vacuum pump. An extra sealing gasket ring (not a standard ISO-100 centering ring) is needed to form a vacuum connection between the Roots blower vacuum pump intake and the ISO-100K fitting (snap ring and sealing gasket rings are sold separately on our Ideal Vacuum web site). These bolt-down intake collar rings are design for ISO-100K flanged fittings to be used with Leybold WA-1001, WAU-1001, WS-1001, and WSU-1001 Roots blower vacuum pumps and have Leybold part number E361 16 121 (replaces older part number 361 16 121).