o2 Spas/Vortex 400 PureZone Filter Cartridge.
Has a closed flat top and the bottom has a fine thread spigot.
Filter dimensions: Height- 210mm(not including spigot), Width- 127mm, Spigot ID- 37mm.
This cartridge is a micron fibre filter that has a finer filtration cycle nearly 10 times more then a normal filter cartridge.
Unit is disposable and recommend to replace every 3-4 months.