Magnum filters Nz made 
Vortex O2 Spas Replacement Cartridge Filter Element
Has a closed top and a fine thread spigot on the bottom.
Used as a replacement element for Vortex O2 Spas.
Filter Dimensions:
Length: 210mm (not including spigot)
Diameter: 127mm
Spigot ID: 36mm
Spigot OD: 42mm
Sold singly