The size of hexagonal bolts can vary depending on the application requirements. Common dimensions include diameter, length, and thread specifications. The diameter of a bolt is usually measured in inches or millimeters, while the length is expressed in units of length, such as inches or millimeters. Internal hexagonal bolts are usually made of high-strength metal materials, such as carbon steel, alloy steel, or stainless steel. The selection of materials depends on the specific application requirements. Internal hexagonal bolts can be surface treated to enhance their corrosion resistance and appearance. Common surface treatment methods include galvanizing, nickel plating, electroplating, etc.