The Tri-X filter is 3-dimensional to more effectively filtrate by depth and surface. The TRI-X Filter is designed to last longer that that of a standard paper filter saving you time, energy, and money in the long run. Tri-X filters will fit on most 1990 to current Hot Spring spa models. Shown on some filters is the number: PN0969601
Dimensions: Diameter 6" Length 10.5" Inside Dia. 1-15/16"
Dimensions: Diameter 6" Length 10.5" Inside Dia. 1-15/16"