Comes with factory certification that the valve will open in the event of a boiler over-pressurizing. This is the most common size thread, but is by no means used in all makes and models; some use a smaller 1/4" version and some a larger 1/2" version.
The image for this product may not accurately represent the actual product shipped. Rest assured that the part will function correctly regardless of it's physical appearance. Each valve has factory printed certifications included in the packaging.