Hex bolt is always made by carbon steel, alloy steel and stainless steel.
Inch series as per ANSI B18.2.1 dimensions always supplied in Grade 5 and Grade 8 according to SAE standard in carbon steel and alloy steel. 18-8 stainless steel hex flanged screws also available.
Metric series carbon steel hexagon bolts generally supplied in class4.8, 8.8, class 10.9 and class 12.9 as per DIN931/933,DIN6914,A325/A325M,A307,A490, BS3692,JIS1181,etc.and ISO standard Nonstandard bolt
Surface treatment could be in black oxide, galvanizing, dacromate. Stainless steel hex flanged bolts also available in SS304 and SS316, Class A2-70 and A4-80.