Metal-Fab 6M12 Style "M" B-Vent 6"x12" Length. These light commercial and residential B-Vents feature a positive twist locking system designed for easy assembly and dis-assembly without bending or harming the product. The B-Vent Locking System comes standard on 3"- 6" pipes. The Metal-Fab 6M12 Style "M" B-Vent 6"x12" Length is ideal for quick installation and long lasting performance. This small sized length is ideal for connecting runs and improving the ventilation throughout the house.