What type of elbow fitting typically requires a cheek piece for proper assembly?

The type of elbow fitting that typically requires a cheek piece for proper assembly is the change cheek elbow. This fitting is unique because it facilitates changes in direction while also accommodating changes in dimensions or cross-sectional shapes, which a cheek piece helps to secure and align properly.

A change cheek elbow allows for more complex transitions in duct systems, and the cheek piece serves to reinforce and stabilize the joint, ensuring that it remains securely connected during operation. These features help prevent air leaks and maintain the integrity of the duct system, which are critical in HVAC applications.

Other types of elbow fittings, such as round, square, and reducer elbows, do not inherently require the use of a cheek piece for assembly. Round and square elbows primarily change the direction of airflow, while reducer elbows transition between different diameters but rely on other methods for secure assembly without the need for a cheek piece.