1/4-20 X 1 HEX HEAD CAP SCREW (HHCS) - (FT) - COARSE - GRADE 8 (GR8) - YELLOW ZINC (YZ)

Hex Cap Screws Grade 8 Course Thread are also sometimes called bolts are considered hardened bolts that are stronger than medium-strength steel screws and they have markings on the top of the head with six 6 radial lines 60 degrees apart.  Grade 8 steel hex head cap screws are SAE J429 specifications and have a tensile strength of 150,000 psi and a proof load strength of 120,000 psi and a "Rockwell Hardness" C33 to C39 according to the manufacturer.