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Stainless steel hex cap screw markings

Inch

  • 18-8 , which can be 302, 303 or 304 stainless, refers to 18% chromium and 8% nickel content.
  • 316 is more corrosion resistant than 18-8 because it contains molybdenum, but in inch fasteners both have the same tensile strength.

Metric

  •  A2 refers to metric 18-8.
  • A4 refers to metric 316.
  • Class 50, 70 and 80 designate increasingly higher metric strength levels.
  • A manufacturer’s mark is required on metric M5 or larger diameters.
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