The light-weight silicone coated fiberglass cloth port covers and removable covers are designed to insulate a 4″ or 6″ port. The special high temperature, flame retardant silicone rubber provides greater life and improves resistance to water/oil, abrasion flexing, tear and puncture. Stack Tester’s Port Cover for 4” & 6” NPT Ports have a heavy duty construction of high temperature fire-retardant materials for many years of trouble free service. Grants tool-less and immediate access to any 4” or 6″ NPT access port while eliminating both leakage and corruption of stack gases.   The removable Port Covers help prevent build-up of condensed stack gas.  Durable Velcro closure provides easy access to the port.  Protect your ports with our specially designed port covers and removable insulated wraps.