This is 3" diameter Z-vent straight pipe with lengths from 6" to 5'. It is stainless steel and used for category II, III and IV heating equipment. Z-Vent is approved as a replacement for high temperature plastic vent. It has simple gasketed connections so no sealant is needed. It freatures the highest pressure rating in the industry. The only metallic special gas vent you can cut to length on site. I can be cut once (cut off not resuable). Made of AL-294C stainless steel and UL approved.