Alloy Steel Socket Head Screws

With a tensile strength of 170,000 psi, these alloy steel screws are stronger than Grade 8 steel screws. Length is measured from under the head.
Black-oxide steel screws are mildly corrosion resistant in dry environments. Zinc-plated steel screws resist corrosion in wet environments.

The screws with a blue-dyed finish are easy to distinguish. Zinc-flake-coated steel screws are 20 times as corrosion resistant as zinc-plated screws and comparable to Dacromet-coated screws.

Zinc-aluminum-coated steel screws are 40 times as corrosion resistant as zinc-plated screws and comparable to Magni-coated screws. They withstand 1,000 hours of salt spray per ASTM B117.
Coarse threads are the industry standard; choose these screws if you don’t know the pitch or threads per inch. Fine and extra-fine threads are closely spaced to prevent loosening from vibration;

the finer the thread, the better the resistance. They are not compatible with coarse threads.
Screws that meet ASTM A574, ASTM A574M, and ISO 898-1 comply with specifications and testing requirements for material quality. Screws that meet ASME B18.3, ASME B18.3M, ISO 21269,

and ISO 4762 (formerly DIN 912) comply with specifications for dimensional standards.