‘Nuts’ is a general term for all types of fasteners with a threaded hole for attachment to a bolt. These are used and included with studbolts and hexagon bolts, for instance. In this case they are delivered standard with a 3.1 certificate and are ‘marked’ with a quality indication and a manufacturer’s logo.
Standard: ANSI B18.2.2
In addition to many different diameters, there are also many different qualities and types available. The quality options are (almost always) those specified in ASTM A194. A distinction is also made between those made of carbon steels and various alloys.