The type and size of hot tub jets vary. They depend on the seating arrangement and hydrotherapy design chosen by the manufacturer. Most hot tub makers use jets from Waterway, CMP, Rising Dragon, or American Products in their models. The types and sizes of jets can range from simple soft water flow with an adjustable nozzle to larger pulsating neck jets. There are also single or twin roto massage jets for different parts of the back.
Brands like Waterway and Balboa provide a wide range of hot tub jet body assemblies. They also offer internal jet replacement parts that are designed for easy replacement. The hot tub jets you need will depend on your spa's brand. Different models use different jets. They can be small 2" directional jets, 3" double spinner jets, or large 5" master massage jets.