Unicel Replacement Filter Cartridge 75 sf Dimension One Spas | 7CH-975Unicel 7CH 975 Replacement Spa Filter Cartridge 7" OD x 10 1 2" Length, 1 1 2" SAE Threaded Bottom (Dimension One Style) The Unicel 7CH 975 is a replacement spa filter cartridge commonly used in Dimension One and similar hot tub filtration systems that require a 7" diameter cartridge with a semi circular top handle and a 1 1 2" SAE threaded bottom connection. Replacing a worn cartridge helps restore circulation, improve water clarity, and reduce