Selkirk Corporation JSC7SA3 7 Inch x 36 Inch Supervent Length 304-alloy Inner Liner 430-alloy Outer has been filling the supply and accessory needs of over 8, 000 sweeps hearth retailers masons and contractors for over 25 years. has the privilege of serving over 80% of the professionals in America.Founded by Robert Daniels Sooty Bob in 1978 has grown from a one-man operation to a national network of six warehouses and a manufacturing plant. From its headquarters in Fairfield Iowa plays a major role in providing for the industry. Size: 7 x 36 . 304-alloy Inner Liner. 430-alloy Outer.