M8*75 Big Head Carriage Bolt Hex Neck DIN 603 Heavy Duty Construction Grade

Big head carriage bolt M8x75

Coach bolts M8x75

Large head coach bolt M8

Big head carriage bolt M8*75

Big head carriage bolt M8x75, also called Coach bolts M8x75 or Large head coach bolt M8. Designed for wood-to-wood fastening, features a smooth domed head, square neck to prevent rotation, and durable zinc-plated finish for corrosion resistance.

Specification

SEODescription

The Big head carriage bolt M8x75, also known as Coach bolts M8x75 or Large head coach bolt M8, is a heavy-duty fastening component designed for structural applications requiring high shear strength and anti-rotation security. Featuring an M8 thread diameter (8mm) and 75mm shaft length, it combines a smooth, dome-shaped enlarged head (typically 16-18mm diameter) with a square neck beneath to prevent turning during installation. Manufactured from grade 4.8/5.8 carbon steel or optional stainless steel (A2/A4), it operates in -50°C to +150°C environments with zinc-plated or hot-dip galvanized corrosion resistance. Widely used in construction, railway infrastructure, agricultural machinery, and wood-to-metal assemblies, its key advantages include tamper-resistant design and load distribution capabilities, though installation requires pre-drilled square-neck holes and proper torque control to prevent head deformation under extreme stress.

SEOSpecification

Parameter	Specification
Product Designation	Big head carriage bolt M8x75 / Coach bolts M8x75 / Large head coach bolt M8
Thread Size	M8 (8mm diameter)
Shank Length	75mm
Head Type	Oval-shaped domed head with square neck
Head Diameter	16.5mm ±0.3mm
Head Height	6.8mm ±0.2mm
Square Neck	5.3mm × 5.3mm
Thread Length	40mm ±2mm
Material Grade	Carbon Steel Grade 8.8
Surface Treatment	Zinc Plated (5-8μm)
Tensile Strength	800 MPa minimum
Torque Value	24-28 N·m (dry)
Standard Compliance	ASME B18.5 / ISO 7412
Application	Wood-to-metal structural connections

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SEOQandA_Product

question:What is the correct torque value for installing M8*75 big head carriage bolt?
answer:Refer to ISO 898-1 standards or manufacturer's torque chart. Typically 20-30 Nm for M8, depending on material.
question:How to prevent bolt head rotation during installation?
answer:Use a wrench to hold the square neck under the bolt head while tightening the nut securely.
question:Can this bolt be used in outdoor/corrosive environments?
answer:Opt for stainless steel (A2/A4) or galvanized variants to prevent corrosion in harsh conditions.
question:Why does the bolt thread strip during assembly?
answer:Ensure matched thread class (6g/6H) between bolt and nut. Avoid cross-threading by aligning components properly.
question:How to address bolt loosening under vibration?
answer:Apply thread-locking adhesive or use a spring washer/nylon-insert nut to maintain tension under dynamic loads.