VP4-18FLEX Noritz Stainless Steel 4" Diameter / 18" Semi-Flexible Vent Pipe The VP4-18FLEXIBLE is a clean and durable stainless steel single wall venting pipe. This 4 in. diameter flexible component is part of the N-Vent system, meaning its components form a perfect seal without the need to tighten. A quick-snap feature allows for easy connections making installation of a professional grade system easier than you would think.Semi-Flexible pipe length.4" Diameter x 18"Semi-Flexible pipe lengthStainless SteelEasy installationProfessional Appearance