Hex cap screws are corrosion resistant 18/8 stainless steel.
Lag bolts, also called lag screws, are basically "large wood screws".
The head is typically an external hex. The materials are stainless steel for corrosion resistance. Lag bolts are used to lag together lumber framing, to lag machinery feet to wood floors, and other heavy carpentry applications.
These fasteners are clearly "screws" when defined by the Machinery's Handbook distinction. The term "lag bolt" has been replaced by "lag screw" in the Machinery's Handbook.
Hex Lag Screws 18-8 Stainless Steel - 1/2" x 4-1/2" Qty-25