Cylindrical head hexagonal screws, also referred to as hexagonal bolts, cup head screws, hexagonal screws, have different names, but the meaning is the same. Generally used hexagonal head screws are also grade 4.8, grade 8.8, grade 10.9, and grade 12.9. Also called hexagonal screws, also called hexagonal bolts. The head is hexagonal head, and it is also cylindrical head. According to the material, it is divided into stainless steel and iron. The stainless steel ones are stainless steel SUS202 inner hexagonal cylindrical head screws. This is made of ordinary stainless steel. There are stainless steel SUS304 inner hexagonal cylindrical head screws and stainless steel SUS316 inner hexagonal cylindrical head screws. The iron ones are divided into strength grades according to the inner hexagonal cylindrical head screw. There are 4.8 inner hexagonal cylindrical head screws, 8.8 inner hexagonal cylindrical head screws, 10.9 inner hexagonal cylindrical head screws, and 12.9 inner hexagonal cylindrical head screws. 8.8-12.9 inner hexagonal cylindrical head screws are called high-strength high-grade inner hexagonal bolts.