Screws onto the cylinder head smog tubes. All California emissions 1967 Cougars with 289 or 390 engines, and 1969 - 1970 Boss 302 Eliminators, all thermactor smog air tubes. Sold individually, two needed per application. Due to the difficulty in removing these valves, we sell them attached to the air supply tubes. These are aftermarket replacements and will look significantly different than the OEM factory installed valves. But they work.