The RV line of Selkirk round vent pipe and fittings is designed for use on approved gas appliances in residential and light commercial and industrial applications. Round vents for large appliances will be found in the QC section which follows.• Size 4"• Part No. 4RV-WT• Measures: 4-5â�„8" x 8-1/4"• Used to ensure clearance to combustibles is maintained• Wall Thimble also serves as a firestop• Adjusts from 4-1/8" to 7" to fit thickness of wall