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Acorn nuts — also widely known as cap nuts or dome nuts — are internally threaded hex fasteners with a closed, domed end that simultaneously secures a bolt or stud and shields the exposed thread from damage, contamination, and corrosion. They are specified wherever thread protection and a clean finished appearance are both required: architectural metalwork, automotive interiors, marine enclosures, HVAC equipment, and electrical panel assemblies all rely on them routinely.
| Material Variants | Stainless Steel (SS 304, SS 316), Carbon Steel, Alloy Steel |
| Grade Options | A2-70, A4-70, Grade 8, Grade 10, Grade 12 |
| Size Range | M3 to M36 / 1/8” to 1-1/2” |
| Thread Type | Metric (Coarse/Fine), UNC, UNF, BSW |
| Standards | DIN 1587, ISO 4032, ASTM A194, BS 3692 |
| Surface Finish | Plain, Zinc Plated, Hot Dip Galvanized, Black Oxide, Passivated |
| Type Variants | Hex Acorn Nuts, Low Crown, High Crown |
| Mechanical Properties | Tensile Strength: 400–800 MPa (depending on grade) |
|
Nominal Size or Basic |
Width Across Flats |
Width Across Corners |
Body Diameter A) |
Overall Height (H) |
Hexagon Height (Q) |
Drill Depth (T) |
Full Thread (U) |
|||
| Max | Min | Max | Min | Max | Min | |||||
| 6 | 0.1380 | 0.3125 | 0.302 | 0.361 | 0.344 | 0.30 | 0.34 | 0.16 | 0.25 | 0.16 |
| 8 | 0.1640 | 0.3125 | 0.302 | 0.361 | 0.344 | 0.30 | 0.34 | 0.16 | 0.25 | 0.16 |
| 10 | 0.1900 | 0.3750 | 0.362 | 0.433 | 0.413 | 0.36 | 0.41 | 0.19 | 0.28 | 0.19 |
| 1/4 | 0.2500 | 0.4375 | 0.428 | 0.505 | 0.488 | 0.41 | 0.47 | 0.22 | 0.34 | 0.25 |
| 5/16 | 0.3125 | 0.5000 | 0.489 | 0.577 | 0.557 | 0.47 | 0.53 | 0.25 | 0.41 | 0.31 |
| 3/8 | 0.3750 | 0.5625 | 0.551 | 0.650 | 0.628 | 0.53 | 0.62 | 0.28 | 0.45 | 0.38 |
| 1/2 | 0.5000 | 0.7500 | 0.736 | 0.866 | 0.840 | 0.72 | 0.81 | 0.38 | 0.59 | 0.50 |
| 5/8 | 0.6250 | 0.9375 | 0.922 | 1.083 | 1.051 | 0.91 | 1.00 | 0.47 | 0.75 | 0.62 |
| 3/4 | 0.7500 | 1.0625 | 1.045 | 1.227 | 1.191 | 1.03 | 1.16 | 0.53 | 0.88 | 0.75 |
|
Nominal Size or Basic
|
Width Across Flats |
Width Across Corners |
Overall Height (H) |
||||
| Max | Min | Max | Min | Max | Min | ||
| 4 | 0.1120 | 0.248 | 0.225 | - | - | 0.200 | 0.177 |
| 5 | 0.1250 | 0.3125 | 0.302 | 0.361 | 0.344 | 0.260 | 0.240 |
| 6 | 0.1380 | 0.3125 | 0.302 | 0.361 | 0.344 | 0.260 | 0.240 |
| 8 | 0.1640 | 0.3125 | 0.302 | 0.361 | 0.344 | 0.260 | 0.240 |
| 10 | 0.1900 | 0.3750 | 0.362 | 0.433 | 0.413 | 0.291 | 0.271 |
| 1/4 | 0.2500 | 0.4375 | 0.423 | 0.505 | 0.482 | 0.338 | 0.318 |
| 5/16 | 0.3125 | 0.562 | 0.545 | 0.650 | 0.621 | 0.385 | 0.365 |
| 3/8 | 0.3750 | 0.625 | 0.607 | 0.722 | 0.692 | 0.432 | 0.412 |
| 7/16 | 0.4375 | 0.673 | 0.659 | 0.775 | 0.750 | 0.680 | 0.660 |
| 1/2 | 0.5000 | 0.750 | 0.736 | 0.866 | 0.840 | 0.572 | 0.552 |
| 9/16 | 0.5625 | 0.875 | 0.861 | 1.010 | 0.982 | 0.482 | 0.462 |
| 5/8 | 0.6250 | 0.938 | 0.909 | 1.083 | 1.037 | 0.807 | 0.787 |
| 3/4 | 0.7500 | 1.12 | 1.08 | - | - | 1.12 | 1.08 |
| 7/8 | 0.8750 | 1.250 | 1.212 | 1.443 | 1.382 | 1.420 | 1.380 |
| 1 | 1.0000 | 1.497 | 1.447 | 1.728 | 1.650 | 1.572 | 1.414 |
Acorn nuts are used to protect exposed bolt threads while providing a secure and visually finished fastening solution across mechanical and structural applications.
Acorn nuts are typically produced through cold forging followed by precision CNC machining to achieve accurate threading and dimensional consistency. Heat treatment processes are applied where required to enhance mechanical strength and durability.
Quality control includes thread gauge inspection, hardness testing, tensile verification, and surface finish evaluation. Each batch undergoes strict dimensional checks to ensure compliance with DIN and ISO standards. KK Fasteners follows structured inspection protocols with full lot traceability, supported by ISO 9001-certified quality systems and adherence to RoHS and REACH compliance requirements.
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Acorn nuts are dome-shaped fasteners with a closed end that fully covers exposed bolt threads. They are used to improve safety, prevent corrosion, and provide a clean, finished appearance in mechanical, structural, and architectural assemblies.
Stainless steel grades such as SS 304 and SS 316 are widely used due to their corrosion resistance, especially in outdoor or marine environments. Carbon steel offers higher strength for structural applications, while alloy steel is preferred for high-stress industrial use.
Acorn nuts are commonly manufactured according to DIN 1587, ISO 4032, and ASTM A194 standards. These ensure consistent dimensions, proper thread fit, and reliable mechanical performance across applications.
Selection depends on environmental exposure, load conditions, and compatibility with mating bolts. Stainless steel is ideal for corrosive environments, while coated carbon steel is suitable for indoor structural use with higher load requirements.
A reliable supplier should offer ISO-certified production, full material traceability, and compliance with international standards. KK Fasteners supports global buyers with consistent quality checks, export documentation, and supply across multiple industries.
