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Carriage bolts are round head, square neck fasteners designed to prevent rotation during installation, making them ideal for wood-to-wood and metal-to-wood connections. Commonly manufactured to standards such as DIN 603, ISO 8677, and ASTM A307, these bolts are widely used in construction, infrastructure, and heavy equipment assembly where secure, tamper-resistant fastening is required.
The square neck beneath the head embeds into the material surface, eliminating the need for holding tools during tightening—an advantage in high-volume assembly or confined installations. Available in stainless steel, carbon steel, and alloy steel grades, carriage bolts provide a balance of mechanical strength and corrosion resistance across indoor and outdoor environments.
KK Fasteners supplies carriage bolts to industrial buyers across multiple sectors, offering consistent dimensional accuracy and material traceability for export-oriented projects.
| Parameter | Details |
|---|---|
| Material Variants | Stainless Steel (SS 304, SS 316), Carbon Steel (Grade 4.6, 5.8, 8.8), Alloy Steel |
| Standards | DIN 603, ISO 8677, ASTM A307, ASTM A325 (custom) |
| Size Range | M5 to M24 | 1/4” to 1” diameter |
| Length Range | 10 mm to 300 mm |
| Thread Type | Metric (Coarse/Fine), UNC, UNF |
| Head Type | Round Head with Square Neck |
| Surface Finish | Zinc Plated, Hot Dip Galvanized, Black Oxide, Plain, PTFE Coated |
| Tensile Strength | 400 MPa – 800 MPa (depending on grade) |
| Hardness | HRB 70–100 (Carbon Steel variants) |
| Thread Coverage | Partially Threaded / Fully Threaded |
|
Basic Bolt Diameter | Body Diameter (E) |
Head Diameter (A) | Head Height (H) | Square Width (O) | Square Depth (P) | |||||
| Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | |
| 8 | .1640 | .157 | .328 | .298 | .102 | .083 | .169 | .155 | .108 | .078 |
| 10 | .1900 | .182 | .436 | .436 | .114 | .094 | .199 | .185 | .125 | .094 |
| 12 | .2160 | .206 | .500 | .468 | .149 | .125 | .215 | .197 | .135 | .105 |
| 1/4 | .2500 | .237 | .594 | .563 | .145 | .125 | .260 | .245 | .156 | .125 |
| 5/16 | .3125 | .298 | .719 | .688 | .176 | .156 | .324 | .307 | .187 | .156 |
| 3/8 | .3750 | .360 | .844 | .782 | .208 | .188 | .388 | .368 | .219 | .188 |
| 7/16 | .4375 | .421 | .969 | .907 | .239 | .219 | .452 | .431 | .250 | .219 |
| 1/2 | .5000 | .483 | 1.094 | 1.032 | .270 | .250 | .515 | .492 | .281 | .250 |
| 5/8 | .6250 | .605 | 1.344 | 1.219 | .344 | .313 | .642 | .616 | .344 | .313 |
| 3/4 | .7500 | .729 | 1.594 | 1.469 | .406 | .375 | .768 | .741 | .406 | .375 |
| Nominal Bolt Size |
Nominal Bolt Length | |||||
| Up to 1" | Over 1" - 2-1/2" | Over 2-1/2" - 4" | Over 4" - 6" | Longer than 6" | ||
| No. 8 - 3/8 | +.02, -.03 | +.02, -.04 | +.04, -.06 | +.06, -.10 | +.10, -.18 | |
| 7/16 & 1/2 | +.02, -.03 | +.04, -.05 | +.06, -.08 | +.08, -.10 | +.12, -.18 | |
| 9/16 - 3/4 | +.02, -.03 | +.06, -.08 | +.08, -.10 | +.10, -.10 | +.14, -.18 | |
|
Nominal Size or Basic Bolt Diameter | Body Diameter (B) |
Head Diameter (W) | Head Height (H) | Square Width (S) | Square Depth (N) | Corner Radius on Square (C) | Fillet Radius (R) | ||||||
| Max | Min | Max | Min | Max | Min | Max | Min | Max | Min | Max | Max | ||
| 1/4 | .2500 | .260 | .213 | .594 | .563 | .145 | .125 | .260 | .245 | .124 | .093 | .031 | .031 |
| 5/16 | .3125 | .324 | .272 | .719 | .688 | .176 | .156 | .324 | .307 | .124 | .093 | .031 | .031 |
| 3/8 | .3750 | .388 | .329 | .844 | .782 | .208 | .188 | .388 | .368 | .156 | .125 | .047 | .031 |
| 7/16 | .4375 | .452 | .385 | .969 | .907 | .239 | .219 | .452 | .431 | .156 | .125 | .047 | .031 |
| 1/2 | .5000 | .515 | .444 | 1.094 | 1.032 | .270 | .250 | .515 | .492 | .156 | .125 | .047 | .031 |
| 5/8 | .6250 | .642 | .559 | 1.344 | 1.219 | .344 | .313 | .642 | .616 | .218 | .187 | .078 | .062 |
| 3/4 | .7500 | .768 | .678 | 1.594 | 1.469 | .406 | .375 | .768 | .741 | .218 | .187 | .078 | .062 |
| Nominal Bolt Size |
Nominal Bolt Length | |||||
| Up to 1" | Over 1" - 2-1/2" | Over 2-1/2" - 4" | Over 4" - 6" | Longer than 6" | ||
| No. 10 - 3/8 | +.02, -.03 | +.02, -.04 | +.04, -.06 | +.06, -.10 | +.10, -.18 | |
| 7/16 & 1/2 | +.02, -.03 | +.04, -.05 | +.06, -.08 | +.08, -.10 | +.12, -.18 | |
| 9/16 - 3/4 | +.02, -.03 | +.06, -.08 | +.08, -.10 | +.10, -.10 | +.14, -.18 | |
| 7/8 & 1 | +.08, -.10 | +.10, -.14 | +.12, -.16 | +.16, -.20 | ||
| 1-1/8 - 1-1/2 | +.12, -.12 | +.16, -.16 | +.18, -.18 | +.22, -.22 | ||
|
Nominal Size or Basic Bolt Diameter | Body Diameter (B) |
Head Diameter (W) | Head Height (H) | Head to Ribs (M) | Number of Ribs | Diameter Over Ribs (V) | Depth Over Ribs (D) | Fillet Radius (R) | |||||||
| Max | Min | Max | Min | Max | Min | Up to 7/8" Length | 1"+ Length | Approx. | Min | Up to 7/8" Length | 1" & 1-1/8" Length | 1-1/4"+ Length | Max | ||
| No 10 | .1900 | .199 | .182 | .469 | .438 | .114 | .094 | .031 | .063 | 9 | .210 | .250 | .407 | .594 | .031 |
| 1/4 | .2500 | .260 | .237 | .594 | .563 | .145 | .125 | .031 | .063 | 10 | .274 | .250 | .407 | .594 | .031 |
| 5/16 | .3125 | .324 | .298 | .719 | .688 | .176 | .156 | .031 | .063 | 12 | .340 | .250 | .407 | .594 | .031 |
| 3/8 | .3750 | .388 | .360 | .844 | .782 | .208 | .188 | .031 | .063 | 12 | .405 | .250 | .407 | .594 | .031 |
| 7/16 | .4375 | .425 | .421 | .969 | .907 | .239 | .219 | .031 | .063 | 14 | .470 | .250 | .407 | .594 | .031 |
| 1/2 | .5000 | .515 | .483 | 1.094 | 1.032 | .270 | .250 | .031 | .063 | 16 | .534 | .250 | .407 | .594 | .031 |
| 5/8 | .6250 | .642 | .605 | 1.344 | 1.219 | .344 | .313 | .094 | .094 | 19 | .660 | .313 | .438 | .625 | .062 |
| 3/4 | .7500 | .768 | .729 | 1.594 | 1.469 | .406 | .375 | .094 | .094 | 22 | .785 | .313 | .438 | .625 | .062 |
| Nominal Bolt Size |
Nominal Bolt Length | |||||
| Up to 1" | Over 1" - 2-1/2" | Over 2-1/2" - 4" | Over 4" - 6" | Longer than 6" | ||
| No. 10 - 3/8 | +.02, -.03 | +.02, -.04 | +.04, -.06 | +.06, -.10 | +.10, -.18 | |
| 7/16 & 1/2 | +.02, -.03 | +.04, -.05 | +.06, -.08 | +.08, -.10 | +.12, -.18 | |
| 9/16 - 3/4 | +.02, -.03 | +.06, -.08 | +.08, -.10 | +.10, -.10 | +.14, -.18 | |
| 7/8 & 1 | +.08, -.10 | +.10, -.14 | +.12, -.16 | +.16, -.20 | ||
| 1-1/8 - 1-1/2 | +.12, -.12 | +.16, -.16 | +.18, -.18 | +.22, -.22 | ||
Carriage bolts are used where a secure, non-rotating fastening solution is required, particularly in wood and composite material assemblies.
Carriage bolts are typically produced through cold forging or hot forging processes, depending on size and material grade. The head and square neck are formed in a single operation to maintain structural integrity and dimensional accuracy. Threads are rolled rather than cut to enhance fatigue resistance and surface finish.
Quality control includes dimensional inspection using calibrated gauges, tensile and hardness testing, and coating thickness verification for plated variants. Lot traceability ensures that each batch can be tracked back to raw material certification.
At KK Fasteners, inspection protocols align with ISO 9001 standards, ensuring consistency across high-volume export orders and compliance with international specifications.
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Carriage bolts are round head fasteners with a square neck directly beneath the head, designed to prevent rotation during tightening. They are commonly used in wood-to-wood or metal-to-wood connections where a smooth, tamper-resistant finish is required.
The best material depends on the application. Stainless steel (SS 304, SS 316) offers corrosion resistance for outdoor or marine environments, while carbon steel grades like 5.8 or 8.8 provide higher strength for structural and load-bearing applications.
Carriage bolts are typically manufactured according to DIN 603 and ISO 8677 standards. Depending on project requirements, they may also comply with ASTM A307 or ASTM A325 for mechanical and structural applications.
Selection depends on load requirements, environmental exposure, and material compatibility. For outdoor or corrosive environments, stainless steel or galvanized bolts are recommended, while high-strength carbon steel is suitable for structural assemblies.
A reliable supplier should offer ISO-certified manufacturing, full material traceability, and proven export experience. KK Fasteners supports global supply with documented quality checks and consistent compliance with international standards.
Consistent dimensional accuracy, controlled material sourcing, and export-ready packaging define the reliability of carriage bolts in critical applications. KK Fasteners supports project-driven procurement with traceable batches and flexible manufacturing capabilities. For technical specifications, bulk pricing, or custom requirements, connect with the engineering team to request a detailed quotation.
