This is an Edwards XDS5, XDS5c, XDS10C, XDS-10, XDS35i & RV3, RV5, RV8, RV12 Gas Ballast Adapter, with 0.25 mm hole. The install instructions manual in pdf format is available for download below. PN A506-26-801.
Fit & Size: Fits Edwards:
Dry Scroll Pumps: XDS5, XDS5c, XDS10, XDS10c, XDS35i
Edwards Part No. A506-26-801.