I'm currently part of the propulsions team for a hybrid rocket project here on campus, working on the liquid fuel injector system. Specifically I'm trying to model which injector designs give us the best burn rate over the entire burn. However, I'm a physics major, not an engineering major, so I'm not familiar with the conventions used in the specifications of the various parts we are using. In particular, is this solenoid valve. I'm trying to determine the interior diameter in the valve through which the fuel will flow, since this will affect the mass flow rate. I see two numbers: 1/4" NPT, and 3/8" orifice size. Can anyone explain to me exactly what these numbers mean? I know the NPT number has to do with the threads on the valve, but i'm not clear on exactly what the two numbers are measuring. I've attached the specifications, these two numbers are in a table on the top of the second page.