Transitions & Connectors - Ducting & Venting - The Home Depot The Master Flow 6 in. 90-Degree Oval Flat The Master Flow 6 in. 90-Degree Oval Flat Elbow is used to change the horizontal direction of a run of oval pipe in an HVAC system. This flat elbow is made of 30-gauge galvanized steel for strength and durability. It can be installed with sheet-metal screws. It Connectors · Reducers[PDF] SHEET METAL CATALOG 820K RETURN AIR 790 DRAW BANDS FLEX DUCT ELBOW 714 DAMPER 090A ANGLE ROUND TO OVAL BOOT 012 OVAL STACKHEAD ROUND DUCT 710R 90° ANGLE REGISTER BOOT 708R STRAIGHT REGISTER BOOT 701 OFFSET COLLAR 776 SCOTTY 265 FLOOR INLET 809 REGULAR STACKHEAD 720 WALL STACK 701 STACK SIDE TAKE OFF 816 1/2".