Countersunk Bolt

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Countersunk Bolt

Countersunk bolts are fasteners with a flat or slightly tapered head designed to sit flush with or below the surface of the material. The head has a conical underside that fits into a matching countersunk hole, providing a smooth and aesthetically clean finish. Countersunk bolts are ideal for applications where protruding bolt heads are not acceptable or where aerodynamics, safety, or appearance are critical.

Types of Countersunk Bolts
  • Flat Head Countersunk Bolt: Standard design for flush installation in metal, wood, or composite materials
  • Oval Head Countersunk Bolt Provides a slightly domed appearance while remaining mostly flush
  • High-Strength Countersunk Bolt: Alloy steel or stainless steel for high-load or critical applications
  • Stainless Steel Countersunk Bolt:: Corrosion-resistant for outdoor or marine

Applicable Standards

Dimensional Requirements:
  • ASME B18.6.6 – Countersunk screws and bolts
  • ISO 2009 / ISO 15071 – Metric countersunk bolts
  • DIN 7991 – Countersunk head screws (hex socket)
  • ASTM A193 / A320 – High-strength bolts for pressure and industrial applications
Material Grades:
  • Carbon Steel (ASTM A36 / A307) – General-purpose
  • Alloy Steel (ASTM A193 B7 / B16) – High-strength applications
  • Stainless Steel (AISI 304 / 316, ASTM A193 B8 / B8M) – Corrosion-resistant
  • Nickel Alloys (Inconel, Monel) – Extreme environments
Material Grades (Commonly Used)

High Tensile, Stainless Steel, Alloy Steel, Inconel, Incoloy, Hastelloy, Monel, Silicon Bronze, Phosphor Bronze, Aluminium Bronze, Nickel, Brass, Copper, Copper Nickel,Duplex, Super Duplex, Titanium Alloys, CB20, Nitronic, Nimonic, ASME, ASTM etc

Typical Specifications
  • Diameter Range: M3 to M36 / ¼” to 1-½”
  • Thread Type: UNC / UNF / Metric (Coarse & Fine)
  • Head Type: Flat or oval head with conical underside
  • Drive Type: Slotted, Phillips, or Hex Socket (Allen)
  • Shank Length As per material thickness and design requirement
Surface Protection / Coating:
  • PTFE Coated (Blue, Yellow, Red, Green & Black)
  • Hot Dip Galvanized
  • Yellow Zinc Plated
  • Blue Zinc Plated
  • Molykote
  • Aluminium Zinc Flake Coated
  • Black Phosphate
  • Zinc Plated
  • Nickel Plated
Engineering Applications
  • Machinery and equipment assemblies requiring flush surfaces
  • Aerospace, automotive, and marine applications
  • Furniture, decking, and cabinetry
  • Structural panels and cladding
  • Electrical and electronic enclosures
Performance & Key Features
  • Flush installation for smooth, safe, and aerodynamic surfaces
  • Prevents snagging or protrusion in high-traffic areas
  • Can be used in high-strength and corrosion-resistant applications
  • Compatible with countersunk washers for load distribution
  • Provides precision alignment in critical assemblies
Design Considerations
  • Ensure countersink angle matches bolt conical angle (commonly 82° or 90°)
  • Proper torque application to avoid crushing material
  • Use washers if additional load distribution is required
  • Material selection based on environment and mechanical load