Magnum filters Nz made 
Spa Quip SQ50
Out Side Diameter - 143mm
Length - 227mm
Bottom End Cap - 53mm hole
Top End Cap - 53mm hole
Fits the following Spas Brand (but not restricted to)
Leisurerite 
Trueform Spas 
Pacific Spas
Forme Leisure
Some aftermarket version can be marked BBF5AA04
Sold singly