This Aluminum 45/60 Degree Adjustable Elbow with 4" Inner Diameter from the Round Gas Vent series is a Type B gas component and consists of the duralock system for a tight seal. Offsets obstructions as needed. Elbows swivel 360° at base. 45°/60° Elbow is adjustable from 0° to 60°. Elbows must be supported when installed.