Hex Drive Size: 3/8"; Width From Flat to Flat: 3/8 inch; Overall Height: 0.157 inch to 0.187 inch; Standard Meets ASME/ANSI B18.16.6
Made of 304 stainless steel (no coating outside) 18-8 which is superior to regular steel and any zinc plated fasteners, provides good strength and corrosion resistance in bad environments.
Will NOT COME LOOSE: With a nylon insert inside, the lock nuts greatly reduce loosening under vibrations and torque.