This exploded view shows a complete water jet from Balboa HydroAir's Gunite range (gunite = concrete). The numbers in the diagram match the numbers in the parts listing below.
To get a good injection of air bubbles by the Venturi effect, the jets should be installed at a maximum water depth of 22 cm, and the distance between the end of the air injector (the little tube in the center of the pipe) and the exit of the jet should be between 7 and 10 cm. You can cut the overall pipe shorter, and/or cut or extend the air injector pipe as needed.
You can also install this type of jet without any air injection, by simply plugging the air entry. You can then install it at greater water depths, for example, without having to worry about the quality of the air injection.