This wall fitting is component of many HydroAir fittings for thin-walled spas, including suctions, skimmers and jets. 

For thicker walled spas, including wooden spas, use the longer version of this fitting.

You can connect various different parts on each end of the wall fitting.

On the inside of the spa, you can screw in a suction cover, or attach a vertical skimmer grille. This wall fitting is also a component of the Eyeball jet.

On the outside of the spa, you can fix it in place with a simple nut and glue it directly to 1 ½" pipe, or screw it into a straight (1 ½" / 50 mm) or elbowed (1 ½" / 50 mm) connector.