These UVCs have a single ended bulb, which is much easier to change than the old strip-light type bulb. They also have a turbulator which forces the water to flow around the bulb in a corkscrew motion to make sure it is all UVed evenly.
Inlet and outlet hose sizes - 20-40mm (0.75"-1.5")
Translucent hosetails let you see if the light is on
Bradshaws Direct (UK) - suppliers of pond liners (pvc and butyl liners), underlay, pond pumps, filters, pond vacuums, fish food, water features and many other water garden accessories.