18-8 stainless steel hex cap screws are manufactured to meet or exceed ASTM F593C and will have a typical composition of 18% chromium and 8% nickel. These percentages exist in 303, 304 and 305 series stainless steels so 18-8 is used at times to designate any and all of those alloy groups. 18-8 stainless steel offers good corrosion resistance and machines easily but will over time stain in coastal environments. They are also acceptable for use in ACQ pressure-treated lumber.

316 stainless steel hex cap screws are manufactured to meet or exceed ASTM F593C. 316 series stainless steel differs from 18-8 by its molybdenum content (2-3%) and a higher nickel content (10-14%). 316 stainless steel has greater corrosion resistance than 18-8 as well as superior strength at high temperatures.

18-8 stainless steel hex tap bolts will have a typical composition of 18% chromium and 8% nickel. These percentages exist in 303, 304 and 305 series stainless steels so 18-8 is used at times to designate any and all of those alloy groups. 18-8 stainless steel offers good corrosion resistance and machines easily but will over time stain in coastal environments. They are also acceptable for use in ACQ pressure-treated lumber.

Finished Hex Nuts in 18-8 stainless steel are designed for use with stainless steel bolts or screws with a specified minimum tensile strength equal or less than the specified proof stress of the mating nut. 18-8 nuts are made from one of the following austenitic alloys: 303, 303SE, 304, XM7, all of which are characterized as having a chromium content of 18% and nickel content of 8-10%. Hardness of Rockwell B95 - C32 for diameters 1/4 through 5/8. Rockwell B80 - C32 for diameters of 3/4 through 1 inch. Proof load of 100,000 psi for diameters 1/4 through 5/8 and 85,000 psi for diameters 3/4 through 1 inch.

Finished Hex Nuts in 316 stainless steel are designed for use with stainless steel bolts or screws with a specified minimum tensile strength equal or less than the specified proof stress of the mating nut. 316 stainless steel differs from 18-8 by it's molybdenum content (2-3%) and a higher nickel content (10-14%). This gives 316 stainless steel a higher degree of corrosion resistance and superior strength at raised temperatures. Hardness of Rockwell B95 - C32 for diameters 1/4 through 5/8. Rockwell B80 - C32 for diameters of 3/4 through 1 inch. Proof load of 100,000 psi for diameters 1/4 through 5/8 and 85,000 psi for diameters 3/4 through 1 inch.