A Hex head cap screw
features a six-sided thick top. Also, the bearing surface has a washer face. The screw is made from medium carbon steel and undergoes heat treatment to harden it further. Hex Head Grade 5 Cap Screws have high tensile strength than say Grade-2 type of screws.
On the other hand, the Grade 8.8 hex head cap screw. Grade 8.8, which also appears as a marking on the bolt, refers to its tensile strength, which is 116,000 psi. The screw is designed for tightening with tools such as spanners and ratchets with sockets.
In both the Grade 5 and 8.8, the screws have unthreaded sections on their shafts
. Moreover, the hexagonal shape on the cap means that you can apply higher torque to the joints you are fastening. Both grades feature carbon steel and heat treatment resulting in increased tensile strength.