Double wall stove pipe is a connector pipe that links wood stoves to insulated chimneys. this system features a black aluminized steel outer casing and heavy-gauge stainless steel inner liner. 1/4 in air space between inner and outer pipes provides great insulating value. 6 in clearance to combustibles. three metal screws supplied with each length. for installed length, subtract 1-3/8 in per joint. listed to ulc s641 and ul 103 standards.