I think the specifications refer to the diameter of the tubing, not the size of the threaded parts of the valve. I could not thread it directly onto the pressure valve and I still don't know exactly what size the threads are. I had to install the solenoid into the run of the air hose line itself and tape it to the side of my co2 tank with electrical tape. The nuts which clamp down over the ends of the air hose after it is fit over the nozzle do seem to make a secure fit. Maybe the brief product description could somehow be amended to include thread sizes. Maybe its just that everyone but me knows what 1/8" FTP implies. The good news is that CO2 doesn't seem to be leaking and it stops bubbling up through the tank whenever the lights go off. Now all I have to do is cut back on my lighting until all the green algae goes away:)