an angle ring is a companion flange which is made out of angle iron. angle iron is rolled into a complete ring and the joint on the ring is welded to make the ring one solid piece. usually angle rings have holes punched in the outer leg so they can bolt up to another ring or a fitting such as an elbow, an expansion joint or a fan or blower. these rings go on to round heavy duty duct work, typically made out of spiral pipe or single longitudinal pipe also known as blow pipe. angle rings are components in air systems where movement of air or movement of material by air is done. they are used in pollution control systems, agricultural equipment such as grain handling and a multitude of other applications. the largest manufacturer and leader of stock and special angle rings in the united states is midwest metal products located in michigan city indiana.