Gas Vent Wall ThimbleAdjusts from 4-1/8 IN to 7 IN to fit thickness of wall.No. 3RV-WT: Size: 3 IN, A = 3-5/8 IN, B = 10-5/8 INNo. 4RV-WT: Size: 4 IN, A = 4-5/8 IN, B = 10-5/8 INNo. 5RV-WT: Size: 5 IN, A = 5-5/8 IN, B = 10-5/8 INNo. 6RV-WT: Size: 6 IN, A = 6-5/8 IN, B = 10-5/8 IN