Hex Cap Nut (Acorn Nut)
Hex cap nuts, also known as acorn nuts, are hexagonal nuts with a closed, dome-shaped end designed to cover and protect exposed bolt or stud threads. The enclosed design prevents damage to threads, enhances safety by eliminating sharp edges, and provides a clean, finished appearance. They are commonly used in applications where both protection and aesthetics are important.
Types of Hex Cap Nuts
- Standard Cap Nut (Low Crown): Short dome for standard applications
- High Crown Cap Nut: Deeper dome to accommodate longer bolt threads
- Stainless Steel Cap Nut: Corrosion-resistant for outdoor and marine use
- Decorative Cap Nut: Polished or plated for aesthetic applications
Applicable Standards
Dimensional Requirements:
- DIN 1587 – Hexagon dome cap nuts
- ASME B18.2.2 (reference for hex dimensions)
- ISO 1587 – Metric cap nuts
- ASTM A563 / ASTM A194 – Material specifications
Material Grades
- Carbon Steel (ASTM A563):General-purpose applications
- Alloy Steel (ASTM A194): Higher strength applications
- Stainless Steel (AISI 304 / 316, ASTM A194 8 / 8M): Corrosion-resistant
- BrassDecorative and electrical applications
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 Parameters
- Diameter Range: M4 to M36 / #6 to 1-½”
- Thread Type: UNC / UNF / Metric
- Head Type: Hexagonal with dome (closed end)
- HeightStandard or high crown depending on application
Surface Finish / Coating:
- PTFE Coated (Blue, Yellow, Red, Green & Black)
- Hot Dip Galvanized
- Yellow Zinc Plated or Cadmium Plated
- Blue Zinc Plated
- Molykote
- Aluminium Zinc Flake Coated
- Black Phosphate
- Zinc Plated
- Nickel Plated
Engineering Applications
- Automotive and mechanical assemblies
- Furniture and decorative fixtures
- Equipment with exposed fasteners
- Electrical panels and enclosures
- Outdoor installations requiring corrosion protection
Performance & Key Features
- Protects exposed threads from damage and corrosion
- Improves safety by covering sharp bolt ends
- Provides clean and aesthetic appearance
- Suitable for light to medium load applications
- Available in corrosion-resistant materials
Limitations
- Not suitable for very long threaded projections (limited dome depth)
- Slightly lower load capacity compared to standard hex nuts (due to closed end)
- Not recommended for high-temperature or pressure-critical applications unless specified
Design Considerations
- Ensure bolt length matches cap depth
- Select appropriate crown height (low or high)
- Match material grade with bolt/stud
- Consider environmental exposure for coating or material selection