Atlantic Fasteners Technical Tips: Hex Cap Screws
Determining Thread Length of Hex Cap Screws
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.
Hex Cap Screw Strength Comparison
¹Amount of force required to pull apart fastener / ²Converted from megapascals (MPa) PSI/145 = MPa or MPa x 145 = PS
Inch
- Grade indicates strength level in the inch system.
- When specifying inch fastener strengths, call them out as grades.
Metric
- Property class indicates strength level in the metric system.
- When specifying metric fastener strengths, call them out as property classes. Don’t confusingly ask for a metric grade 8 hex cap screw. Ask for a metric property class 10.9 instead
Warning: Similar numbers used for grade and property class designations don’t stand for the same strength. For example, a Grade 8 hex cap screw and a property class 8.8 hex cap screw have different tensile strengths.
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