Designed for appliances tested and listed for DirectVent. Features a fully unitized twist-lock construction in both 4" x 6 5/8" and 5" x 8" vent sizes. Use of sealant is optional, unless specified by the appliance manufacturer. To calculate install length, subtract 1 1/2" for each joint. No beads or hems. Black pipe lengths feature exterior laser-welded seams.