In your tolerances, there is a case where you have zero zero off from the base dimensions. That means you cannot assemble or have very difficult time to assemble, even though the parts are made to the spec.
The clearance is determined by what kind of movement you have to have with the two...
Eductor seems often used for liquid, and transvector, or venturi or ejector is for air or gas. Anyway, as JeffHofacre suggests, go for off-the-shelf products, that you can find suppliers' web sites such as www.foxvalve.com, www.iprocessmart.com/itw/transvector_airjet.htm etc. Good to use a...
