What are special points or lines used in layout that don't fall on regular element lines known as?

The term used for special points or lines in a layout that do not align with the regular element lines is "auxiliary lines or points". Auxiliary lines are often employed in drafting and design to assist in creating complex shapes or details that are not easily represented by the primary elements of the drawing. They provide reference points that help in establishing dimensions, angles, or other features without being a part of the final design itself.

Using auxiliary lines allows for more accurate designs and aids in visualizing relationships between different components of a system. This technique is commonly utilized in HVAC sheet metal layout to ensure that all parts fit together properly and function efficiently. Auxiliary lines enhance clarity in the design process, making it easier to communicate ideas and measurements to others involved in the project.