Clarathon 2 PACK Spa Filter Cartridges for: Aero Spa, Aqua, GoPlus, Blue Wave, Swim Time, TheraPure, Therma Spa, Thera-Spa Pack of (2) filter cartridges Length: 3-1/2" - Width: 4" -Top: Closed Bottom: 2-1/2" Inside Female Threads (2-5/8" outside diameter) Genuine Clarathon Filters - not cheap knock-offs 2- pack. STOCK UP & SAVE!!