DIN 603 Carriage Bolts | Mushroom Head Square Neck Bolts
DIN 603 Carriage Bolts are distinguished by their smooth mushroom-shaped head and square neck, with each feature serving a specific purpose during assembly. The domed head provides a low-projection, finished surface on the exposed side of the joint, while the square neck engages with the material and prevents the bolt from turning when the nut is tightened. This allows the fastener to be installed without needing to hold the bolt head with a wrench during normal assembly.
The square neck also helps maintain the bolt’s position after installation, making DIN 603 particularly useful for joints where the fastener head remains visible or accessible from only one side. Different diameters, lengths, materials, and finishes are available to match the thickness of the connected components and the required service environment.
Specification:
The specification of DIN 603 Carriage Bolts covers the dimensions, materials, and mechanical property classes required for different fastening conditions. Standard diameters range from M5 to M20, with bolt length selected according to the thickness of the connected components. Key dimensional requirements include bolt diameter, length, thread length, head diameter, head height, and square neck dimensions.
For carbon steel and alloy steel versions, DIN 603 carriage bolts can be supplied in property classes 4.8, 8.8, 10.9, and 12.9 according to size and production requirements. Stainless steel options include A2-70 and A4-70, with A4-70 providing better corrosion resistance for demanding environments. Surface finishes such as plain, zinc plated, hot-dip galvanized, and customized coatings are available according to the material and application.
| Item | Specification |
|---|---|
| Standard | DIN603 |
| Product Type | Carriage Bolt/Mushroom Head Square Neck Bolt |
| Head Type | Mushroom Head |
| Neck Type | Square Neck |
| Diameter | M5-M20 |
| Length | 16-200mm |
| Thread | Metric Coarse Thread |
| Material | Carbon Steel,Alloy Steel,Stainless Steel |
| Property Class | 4.8,8.8,10.9,12.9 |
| Stainless Steel Grade | A2-70,A4-70 |
| Surface Treatment | Plain,Zinc Plated,Hot Dip Galvanized,Bright Finish,Passivation |
Dimension Chart of DIN603 Mushroom Head Square Neck Bolts:
The DIN 603 dimension chart shows the measurements that determine how a carriage bolt fits into the mating hole and sits against the connected surface. In addition to the nominal diameter and bolt length, the head diameter and head height define the footprint of the mushroom head, while the square neck width and neck height determine how the bolt seats in the material and resists rotation during tightening. DIN 603 carriage bolts are available from M5 to M20 in different lengths to accommodate varying material thicknesses and joint configurations. When selecting a size, the bolt diameter should correspond to the prepared hole, while the bolt length should provide sufficient thread engagement beyond the connected parts. The dimension chart can be used to compare head diameter, head height, square neck dimensions, and threaded length for each available size.
| Mon | M5 | M6 | M8 | M10 | M12 | M16 | M20 |
| P | 0.8 | 1 | 1.25 | 1.5 | 1.75 | 2 | 2.5 |
| dk max | 13.55 | 16.55 | 20.65 | 24.65 | 30.65 | 38.8 | 46.8 |
| dk min | 12.45 | 15.45 | 19.35 | 23.35 | 29.35 | 37.2 | 45.2 |
| ds max | 5 | 6 | 8 | 10 | 12 | 16 | 20 |
| ds min | 4.52 | 5.52 | 7.42 | 9.42 | 11.3 | 15.3 | 19.16 |
| k1 max | 4.1 | 4.6 | 5.6 | 6.6 | 8.75 | 12.9 | 15.9 |
| k1 min | 2.9 | 3.4 | 4.4 | 5.4 | 7.25 | 11.1 | 14.1 |
| k max | 3.3 | 3.88 | 4.88 | 5.38 | 6.95 | 8.95 | 11.05 |
| k min | 2.7 | 3.12 | 4.12 | 4.62 | 6.05 | 8.05 | 9.95 |
| r max | 0.5 | 0.5 | 0.5 | 0.5 | 1 | 1 | 1 |
| s max | 5.48 | 6.48 | 8.58 | 10.58 | 12.7 | 16.7 | 20.84 |
| s min | 4.52 | 5.52 | 7.42 | 9.42 | 11.3 | 15.3 | 19.16 |
Application of DIN603 Mushroom Head Square Neck Bolts:
The choice of DIN 603 Carriage Bolt depends on the load, environment, and material of the connected components. Carbon steel grades 4.8 are suitable for general-purpose assemblies such as agricultural machinery frames, equipment guards, metal brackets, and trailer components, while 8.8 and higher-strength 10.9 or 12.9 versions can be selected for more heavily loaded joints in machinery frames, conveyor systems, structural equipment, and heavy-duty mechanical assemblies. Zinc-plated finishes are commonly used for indoor or moderately corrosive conditions, while hot-dip galvanized carriage bolts are better suited to outdoor structures, agricultural equipment, fencing systems, and trailers exposed to weather.
Stainless steel DIN 603 carriage bolts provide a different combination of strength and corrosion resistance. A2-70 is suitable for outdoor equipment, food-processing machinery, electrical enclosures, and general stainless steel assemblies exposed to moisture, while A4-70 is preferred for marine equipment, coastal installations, chemical-processing machinery, and other environments with higher chloride or corrosion exposure. The smooth mushroom head is particularly useful on equipment panels, guards, timber structures, and accessible surfaces where a low-projection and clean finished appearance is required.