4) Pentair 172855 FNS Nautilus Swimming Pool DE Filter Air Vent Relief Screens 4 Pentair 172855 3/4" Stainless Steel Replacement Air Vent Strainers Air vent strainer replacement Fits Pentair Nautilus Plus pool and spa D.E. filters Also fits Pentair FNS, FSH pool and spa D.E. filters Made of stainless steel