Selkirk 90 Degree Adjustable Elbow Type B Od = Id = 1/2 Inner Wall Aluminum, Outerwall Galvanized For Gravity Draft Venting Of Listed Lp Or Natural Gas Burning Appliances 100 Million Btu Per Hr., 500 Deg. F Max. Appropriate For Thru The Wall Where Applicable Not For Wall Furnaces Ul Listed 10 Yr. Warranty Boxed #4rv-el90 4 Price is indicated for bulk discounted quantity of 2 unit(s) per case. 4" ,Type B gas vent ,OD = ID = 1/2" ,Inner wall aluminum outerwall galvanized ,For gravity draft venting of "listed" LP or natural gas burning appliances ,100 million BTU per hr. 500 deg. F max. ,Appropriate for thru the wall where applicable ,Not for wall furnaces ,UL listed ,10 yr. warranty ,Boxed ,#4RV-EL90 ,4"