Air traveling through a duct is slowed up when it encounters a right angle turn of an elbow or a T shaped fitting.. This "slow-up" can disrupt the air flow and is detrimental to the efficiency of the duct system. Therefore air turning vane assemblies are used to guide air evenly around such turns. These assemblies are comprised of turning vanes, which are often fabricated by the contractor, and rails which are supplied by the manufacturer with embossing and pre-stamped slots to position the turning vanes.