New water neck ("cap") for an Opel Thermostat Housing. Fits on all CIH 1.5L, 1.9L and 2.0L thermostat housings including the 1975 EFI housing as well as the later 2.0L EFI systems. Excellent addition to the PN #11037 Thermostat Base. See PN 6013 gasket and PN 11005 thermostat.