Hexagon Socket Head Capscrews are a type of bolt similar to the DIN 912. They are usually delivered standard with a 3.1 certificate and are ‘marked’ with a quality indication and a manufacturer’s logo.
Standard: ANSI B18.3
The diameters are specified in inches (f.e. 5/8”). For bolts with a metric diameter (f.e. M16) but an ASTM quality, there are generally somewhat fewer options and those that are available do not fall under the ANSI B18.3.
Hexagon socket head capscrews can be obtained in many different diameters and many different qualities and types.