This lid suits Spa-Quip 2000, Aquaswim, Monarch Ecopure, some Davey's, Hurlcon, Stroud, Poolrite-Enduro. Diameter 215mm.
Older styles will also need a new pressure refief valve as the thread is now finer.
The thread is the same now as the pressure gauge side. If your refief valve thread is courser, you will need the new valve.
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