Atlantic Fasteners Technical Tips: Hex Cap Screws

Determining Thread Length of Hex Cap Screws

Stainless Steel Hex Cap Screw Markings


  • 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.


  • 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


  • Grade indicates strength level in the inch system.
  • When specifying inch fastener strengths, call them out as grades.


  • 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. 

Visit Us in Person or Submit your Questions Below


Hours: Mon. - Fri. 7am - 5pm

92 H.P. Almgren Drive
P.O. Box 1068
Agawam, MA 01001
1-800-800-BOLT (2658)
413-785-5770 Fax


Search engine powered by ElasticSuite