Carriage bolt | A4 | DIN 603
Do you need a carriage bolt that works safely even in damp, salty, or chemically harsh environments? Carriage bolt DIN 603 A4 in A4 / AISI 316 acid-proof stainless steel is built to resist corrosion and maintain strength over a long period. The round, smooth head with a square neck underneath provides a secure grip in wood and prevents the bolt from rotating when tightened. The combination of high corrosion resistance and strong construction makes it ideal for long-term use in tough environments.
AREA OF APPLICATION
Perfect for fastening in wood, metal fittings, marine equipment, and structures in coastal areas, jetties, ships, outdoor constructions, and the food industry. The square neck under the head locks the bolt against the substrate, providing a stable and vibration-proof connection without the need to hold it with tools. Easily installed together with a nut and washer and requires minimal maintenance even with continuous exposure to moisture and salt.
TECHNICAL SPECIFICATIONS
Product type: Carriage bolt
Standard: DIN 603
Grade: A4 / AISI 316 acid-proof stainless steel
Material class: A4-70
Thread type: Metric (ISO thread)
Surface treatment: Untreated (natural colored stainless steel)
Head shape: Round dome head with square neck
Grip type: Not applicable
FREQUENTLY ASKED QUESTIONS (FAQ)
What characterizes a carriage bolt (DIN 603) and how does it work?
A carriage bolt is a classic fastening component for wood and steel structures:
-
Dome-shaped smooth head without tool recesses: The arched, smooth head provides a clean finish without sharp edges. Because it lacks screw recesses (such as Phillips or Torx), unauthorized removal from the outside is made difficult, which provides theft and vandal-proof fastening.
-
Self-locking square neck: Directly below the dome head is a square neck. When the bolt is pulled into a pre-drilled wooden hole, the neck is pressed into the wood fibers and prevents the bolt from rotating when the nut is tightened from the back.
-
Through-mounting: Installed through pre-drilled holes and secured on the back with a stainless washer and nut (or lock nut).
Why is acid-proof stainless steel A4 (AISI 316) the best material choice?
A4 steel (1.4401 / AISI 316) contains molybdenum, which provides superior protection in extremely demanding environments:
-
Maximum protection in piers and marine environments: Withstands constant contact with salt water, brackish water, crevice corrosion, and harsh coastal climates without suffering from rust or pitting.
-
Resistant to chemicals and pressure-treated timber: Resists the corrosive copper salts found in modern pressure-treated timber (NTR-A/NTR-AB) as well as ammonia in agriculture and stables.
-
No corrosion contagion: The material does not shed rust stains that discolor the wood around the attachment point.
What should you keep in mind when installing A4 carriage bolts in wood or steel?
-
Correct hole diameter for pre-drilling: Drill the hole with the same diameter as the bolt's threaded stem. Do not drill too large, or the square neck will lose its grip in the wood.
-
Mounting in steel: When mounting where the bolt goes through steel plate, the receiving hole in the steel must have a punched or filed square hole so that the square neck can sink in and lock.
-
Use a large washer on the back: Always install a heavy-duty fender washer or repair washer (A4) under the nut on the back against the wood surface. This prevents the nut from being pulled into and crushing the wood fibers during tightening.
-
Lubricate the thread before tightening: Use a thin layer of assembly paste or lubricant on the A4 thread to prevent seizing/galling when tightening the A4 nut.
