Spa OEM's - The companies who assemble the spa you may own generally do not make their own components. Fittings such as jets are bought from suppliers who specialize in manufacturing the fittings and small parts needed to assemble the tub.
If there are no identifiable markings, part numbers or logos on the jet parts you can try to visually determine which brand you might have.
The rear of each jet is shown because the front faces are aesthetic and only give an indication to the series the jet belongs to not the brand.
The rear of the jet is called the diffuser, each brand has their own design which specific to their jet bodies. They are not interchangeable with other brands.
5" Jet Faces
Note - CMP & Waterway Diffusers appear similar, pay close attention when examining your jets.