These are very widely used by a number of spa manufacturers. These are available in a number of colors and styles.
Poly jets screw into the jet wall fitting with the very fine threads shown in this photo.
This jet has a directional nozzle.
Material
Plastic
Face Diameter
3-1/2"
Length
3-3/4"
Hole Size
2-5/8" (For Wall Fitting) This is a part of the jet body and is not shown here.
Markings
"218-6010" is molded on back of the face