Ideal for plugging/sealing the test port openings on the oven vents after a combustion analysis has been performed. Provide a clean, professional approach to sealing inspection ports on furnace/boiler flues. Holes do not need to be sealed with high temperature RTV foil tape. For high efficiency ovens and boilers in test ports, purchase 1/4 inch NPT threaded nylon plugs and an appropriate size tap and die. This hole/plug size is designed for use with the ECOM-D Combustion Analyzer and the Wohler A550.