If you were to explain the difference between LWN and WN flange to a … HH and X are usually equal and X is defined in ASME B16.5.

The key types of flanges are the welding neck, long welding neck, slip-on, socket weld, lap joint, threaded and blind flanges. In addition to these standard flanges, some special ones exist, called Weldoflange/Nipoflange and Elboflange, swivel flange, expander/reducer flange, and orifice flanges.