Hex head cap screws feature a thick, hexagonal head with a washer face under the head to provide an ample bearing surface for tightening with a wrench. They are general-purpose threaded fasteners designed for insertion in pretapped holes or for use with nuts.

Materials

Alloy Steel—contains enough alloying elements (other than carbon) to affect properties such as tensile strength; generally more responsive to heat and mechanical treatments than plain carbon steels.

Aluminum—corrosion- and moisture-resistant material; excellent for outdoor use. Provides the strength of mild steel at only one-third the weight. Nonmagnetic.

Brass—alloy of copper and zinc that resists rust and moderate atmospheric corrosion. Not high in strength, but is durable and conducts electricity. Often used for appearance. Nonmagnetic.

Nickel Copper Alloy—a corrosion-resistant metal alloy with excellent thermal conductivity, but slightly decreased electrical conductivity when compared to copper. Strong and fatigue-resistant.

Silicon Bronze—an alloy of copper and tin with higher strength and hardness than brass and with silicon diffused into the metal at an elevated temperature. Very ductile with a high resistance to repeated stresses, corrosion, and fatigue.

Stainless Steel—contains a minimum of 12% chromium for exceptional resistance to extreme environmental conditions. Properties are highly anticorrosive. Not affected by scratching; however, not as strong as common alloy steels. May be mildly magnetic.

18-8 Stainless Steel—contains approximately 18% chromium and 8% nickel. Provides excellent protection against rust and corrosion. The material of choice for prolonged outdoor use or exposure to salt spray and chemical fumes. May be mildly magnetic. Comparable to ASTM 300 Series and ISO A2.

316 Stainless Steel—contains a minimum of 2% molybdenum for superior corrosion resistance and reduced risk of pitting in extreme environments. Is nonmagnetic and can't be heat treated or hardened. Comparable to ISO A4.

Steel—the most common fastener material. Available in these types:

• Alloy Steel contains enough alloying elements (other than carbon) to affect the fastener's properties; generally more responsive to heat and mechanical treatments.
• Plain Steel (or Carbon Steel) contains only carbon and residual amounts of any other impurities. It is magnetic and malleable and can be either cast or wrought.

Steel fasteners are classified by Grade (for SAE) or Property Class (for metric):

Grade 1/Property Class 4.6—low strength
Grade 5/Property Class 8.8—medium strength
Grade 8/Property Class 10.9—high strength
Grade 9/Property Class 12.9—high-grade AISI 8640H alloy steel