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Round Head Carriage Bolts

Round Head Carriage Bolts - Premium Fastening Solutions

Round head carriage bolts are one of the most recognizable and widely used fasteners across construction, woodworking, and industrial assembly. Recognized by their smooth, domed head and a square neck directly beneath, these bolts deliver a tamper-resistant, clean appearance while providing exceptional holding power. The round head creates a low-profile finish that resists snagging and is often specified for outdoor structures, furniture, fencing, trailer decks, and playground equipment where safety and visual appeal matter.

Why Our Round Head Carriage Bolts Stand Out

Every bolt we supply is manufactured to stringent standards, ensuring consistent thread fit, precise square neck dimensions, and reliable tensile performance. Whether you are securing a ledger board, assembling a swing set, or constructing heavy-duty pallets, these bolts simplify single-wrench installation. The square neck seats firmly into a pre-drilled or punched square hole, preventing rotation while the nut is tightened from the opposite side. This design eliminates the need for a second wrench on the head side, saving time and labor during assembly.

Low-profile round head for a finished, snag-free surface
Square neck locks into wood or metal to resist spinning
Available in multiple grades for structural and light-duty uses
Corrosion-resistant coatings suited to indoor and outdoor environments
Conforms to ASME B18.5 and DIN 603 specifications
Full and partial thread options to match material thickness

Detailed Product Specifications

Our round head carriage bolts are offered in an extensive range of diameters and lengths, with unified coarse (UNC) and metric coarse (ISO) threading. Choose from standard steel, high-strength carbon steel, and stainless steel alloys to meet project requirements. Multiple finishes protect against rust and oxidation, and custom packaging options are available for high-volume orders. The table below outlines the primary dimensional data for our most requested sizes.

Nominal Diameter (inch/mm)	Thread Pitch (tpi/mm)	Length Range (inch/mm)	Head Diameter (inch/mm)	Head Height (inch/mm)	Square Neck Width (inch/mm)
1/4" (6.35 mm)	20 tpi (1.27 mm)	3/4" – 10" (19 – 254 mm)	0.594" (15.1 mm)	0.145" (3.7 mm)	0.260" (6.6 mm)
5/16" (7.94 mm)	18 tpi (1.41 mm)	1" – 12" (25 – 305 mm)	0.719" (18.3 mm)	0.176" (4.5 mm)	0.324" (8.2 mm)
3/8" (9.53 mm)	16 tpi (1.59 mm)	1" – 14" (25 – 356 mm)	0.844" (21.4 mm)	0.208" (5.3 mm)	0.388" (9.9 mm)
1/2" (12.7 mm)	13 tpi (1.95 mm)	1-1/2" – 20" (38 – 508 mm)	1.094" (27.8 mm)	0.270" (6.9 mm)	0.515" (13.1 mm)
5/8" (15.88 mm)	11 tpi (2.31 mm)	2" – 24" (51 – 610 mm)	1.344" (34.1 mm)	0.344" (8.7 mm)	0.642" (16.3 mm)
3/4" (19.05 mm)	10 tpi (2.54 mm)	2-1/2" – 30" (64 – 762 mm)	1.594" (40.5 mm)	0.406" (10.3 mm)	0.768" (19.5 mm)

Material and Finish Options

Select from three core material grades to match environmental and load conditions. Zinc-plated steel provides economical corrosion resistance for general interior use. Hot-dip galvanized bolts withstand decades of outdoor exposure in contact with pressure-treated lumber. Stainless steel (18-8 and 316) ensures maximum resistance against chemicals, salt spray, and moisture, making them the top choice for marine and food-grade applications.

Material Grade	Finish / Coating	Tensile Strength	Typical Applications
Low Carbon Steel (Grade 2)	Zinc Plated, Clear or Yellow	60,000 psi min	Furniture, general wood assembly, indoor projects
Medium Carbon Steel (Grade 5)	Zinc Plated or Hot-Dip Galvanized	120,000 psi min	Decks, docks, structural framing, heavy machinery guards
Stainless Steel 18-8 (A2)	Plain, Passivated	70,000 – 100,000 psi	Outdoor playgrounds, food processing, chemical plants
Stainless Steel 316 (A4)	Plain, Passivated	70,000 – 100,000 psi	Saltwater marine, coastal construction, pharmaceutical

Thread Configuration and Packaging

Standard round head carriage bolts feature a full body diameter under the head for a length equal to the square neck and a short unthreaded shoulder, followed by partial threading. Full-thread versions are available on special order for applications where the clamped material thickness is consistently near the bolt length. Lengths are measured from under the head to the end of the bolt. Bulk packaging in 25, 50, and 100-piece boxes, as well as contractor pails and pallet quantities, streamlines jobsite distribution. Custom kitting with matching hex nuts and flat washers reduces sourcing complexity.

All sizes comply with current ASTM, ASME, and DIN standards, and lot traceability is maintained from raw material to finished fastener. Request a sample or quote for your specific diameter, finish, and quantity needs.

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Round Head Carriage Bolts