DuraVent 4PVP-KHA 4" Inner Diameter - PelletVent Pro Type L Chimney Pipe - Double Walled, Black and Stainless Steel,M&G DuraVent,4PVP-KHA" /> It has the duralock tightening system, to get a tight fit This is a 4" Horizontal Kit, this is from the PelletVent Pro Line The Kit Includes: Round Horizontal Cap, Wall thimble, and Appliance Adapter that increases 3"-4"