Cylindrical head hexagon socket bolt, also known as hexagon socket bolt, cup head screw. The commonly used hexagon socket head bolts are 4.8 grade, 8.8 grade, 10.9 grade, and 12.9 grade. According to the material, there are stainless steel and iron. According to the strength grade of hexagonal socket head bolts, there are 4.8, 8.8, 10.9, and 12.9 grade hexagonal socket head bolts made of iron. Grade 8.8-12.9 hexagon socket head screws are called high-strength hexagon socket bolts.