SELKIRK CORP 187703 3-Inch Wall Thimble Product Description 3", 3RV-WT, Wall Thimble. Adjusts 4-1/8" to 7" to fit wall thickness. Round Type B gas vent. When installed according to manufacturer specifications, the wall thimble provides the required 1 inch air space to combustibles. Tested and listed per UL-441 for installation as type "B" and B-W gas vents to be installed in single and multi-story buildings. From the Manufacturer 3", 3RV-WT, Wall Thimble. Adjusts 4-1/8" to 7" to fit wall thickness. Round Type B gas vent. When installed according to manufacturer specifications, the wall thimble provides the required 1 inch air space to combustibles. Tested and listed per UL-441 for installation as type "B" and B-W gas vents to be installed in single and multi-story buildings. Features 3", 3RV-WT, Wall Thimble Adjusts 4-1/8" to 7" to fit wall thickness Round Type B gas vent When installed according to manufacturer specifications, the wall thimble provides the required 1 inch air space to combustibles Tested and listed per UL-441 for installation as type "B" and B-W gas vents to be installed in single and multi-story buildings USA SHIPPING estimates delivery times and we work to get your item to you as quickly as possible and within those times, but please know it may take slightly longer than the estimate.