Pentair 074923 18-Inch Element Replacement SM and SMBW Pool and Spa D.E. Filter Element replacement Fits Pentair SM & SMBW 4000 series D.E. pool and spa filter model 4036 Also fits Pentair SM & SMBW 2000 series D.E. pool and spa filter model 2036 The SM and SMBW 2000 & 4000 DE Filters require 8 Elements One element, 8 elements are required to make a set