What is the turned under edge or horizontal portion of the header called?

The correct identification of the turned under edge or horizontal portion of the header is referred to as the header flange. The header flange serves a significant structural and aesthetic function, providing support and a finished look to the header that is often found in various types of construction and fabrication.

The header flange helps in distributing loads and can also play a role in making certain designs more durable. Its design allows for easy connection to other structural elements, making it a crucial component in the stability and functionality of the overall structure.

In contrast, the other options reflect different terminology that does not accurately describe this specific feature. The header rim typically refers to the outermost edge or border, which is distinct from the turned under aspect. The header edge might imply a more general reference to any edge of the header without specifying the turned under part. The term header lip often describes a specific show of material at the edge of something but does not align with the technical definition of the turned under portion in this context. Thus, header flange is the term that correctly identifies this key feature in construction terminology.