Fasto DIN 603 Carriage Bolt Round Head Square Neck | Galvanized & 304 SS
Product Introduction
What it is a carriage bolt？
A carriage bolt is four parts in one piece: a smooth dome head, a square neck right under it, a plain shank, and a threaded section. The head has no screwdriver slot and no hex flats — it's not made to be turned. It's made to sit flush on the surface while the square neck digs into the base material and locks the bolt in place.
Why the square neck matters
Tighten the nut and the square section bites into the wood or soft metal. The bolt can't rotate with the nut, so you never need to hold the head from the other side. One person, one wrench, done. That single feature is the whole reason these bolts exist — it's why timber decks, fence posts and farm jigs use them instead of hex bolts.
One honest warning: the square neck only works when the base is softer than the neck. Push it through hard steel and it just spins. For steel-to-steel you want the ribbed or fin neck series, or a hex bolt with a wrench on both ends.
How length is measured
From the underside of the head — the root of the square neck — to the tip of the thread. The dome is not counted. This trips up more buyers than any other detail. A "2 inch" carriage bolt with the head included is not a 2 inch carriage bolt.
What you get in the box
Bolt, hex nut, flat washer. We can pack them as loose bolts, as matched sets, or bagged kits with the nut and washer already on. For fence and deck kits, bagged sets sell better at retail; for workshops, loose boxes are what they want. Tell us how you sell and we'll pack accordingly.
Full Specification
1 Metric dimensions — ISO 8677:1986 / GB/T 14 (mm)
| Thread d | Pitch P | Head dia. dk | Head hgt. k | Square width v | Square len. f | Thread len. b | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| max | min | max | min | max | min | max | min | L ≤ 125 | 125 < L ≤ 200 | L > 200 | ||
| M5 | 0.8 | 13.0 | 11.9 | 3.1 | 2.5 | 5.48 | 4.52 | 4.1 | 2.9 | 16 | 20 | — |
| M6 | 1.0 | 16.0 | 14.9 | 3.6 | 3.0 | 6.48 | 5.52 | 4.6 | 3.4 | 18 | 24 | — |
| M8 | 1.25 | 20.0 | 18.7 | 4.8 | 4.0 | 8.58 | 7.42 | 5.6 | 4.4 | 22 | 28 | 41 |
| M10 | 1.5 | 24.0 | 22.7 | 5.8 | 5.0 | 10.58 | 9.42 | 6.6 | 5.4 | 26 | 32 | 45 |
| M12 | 1.75 | 30.0 | 28.7 | 6.8 | 6.0 | 12.70 | 11.30 | 8.8 | 7.2 | 30 | 36 | 49 |
| M16 | 2.0 | 38.0 | 36.4 | 8.9 | 8.0 | 16.70 | 15.30 | 12.9 | 11.1 | 38 | 44 | 57 |
| M20 | 2.5 | 46.0 | 44.4 | 10.9 | 10.0 | 20.84 | 19.16 | 15.9 | 14.1 | 46 | 52 | 65 |
2 Inch dimensions — ASME B18.5, round head square neck (in)
| Nominal size | Shank E | Head A | Head H | Square O | Square P | |||||
|---|---|---|---|---|---|---|---|---|---|---|
| max | min | max | min | max | min | max | min | max | min | |
| #8 (.164) | .1640 | .157 | .328 | .298 | .102 | .083 | .169 | .155 | .108 | .078 |
| #10 (.190) | .1900 | .182 | .436 | .436 | .114 | .094 | .199 | .185 | .125 | .094 |
| #12 (.216) | .2160 | .206 | .500 | .468 | .149 | .125 | .215 | .197 | .135 | .105 |
| 1/4 (.250) | .2500 | .237 | .594 | .563 | .145 | .125 | .260 | .245 | .156 | .125 |
| 5/16 (.3125) | .3125 | .298 | .719 | .688 | .176 | .156 | .324 | .307 | .187 | .156 |
| 3/8 (.375) | .3750 | .360 | .844 | .782 | .208 | .188 | .388 | .368 | .219 | .188 |
| 7/16 (.4375) | .4375 | .421 | .969 | .907 | .239 | .219 | .452 | .431 | .250 | .219 |
| 1/2 (.500) | .5000 | .483 | 1.094 | 1.032 | .270 | .250 | .515 | .492 | .281 | .250 |
| 5/8 (.625) | .6250 | .605 | 1.344 | 1.219 | .344 | .313 | .642 | .616 | .344 | .313 |
| 3/4 (.750) | .7500 | .729 | 1.594 | 1.469 | .406 | .375 | .768 | .741 | .406 | .375 |
3 Material & property classes
| Class | Material | Tensile Rm (MPa) | Yield (MPa) | Typical use |
|---|---|---|---|---|
| 4.6 | Low carbon steel | 400 min | 240 min | Fences, furniture, light framing |
| 4.8 | Low carbon steel | 400 min | 320 min | General timber work — most common spec |
| 5.6 / 5.8 | Medium carbon steel | 500 min | 300–400 min | Heavier timber, metal-to-wood |
| 8.8 | Alloy steel, Q&T | 800 min | 640 min | Heavy-duty and structural auxiliary joints |
| 10.9 | Alloy steel, Q&T | 1040 min | 940 min | High-strength industrial (made to order) |
| A2-70 / A4-70 | Stainless 304 / 316 | 700 min | 450 min | Coastal, humid, food & chemical |
| A2-80 | Stainless, cold-worked | 800 min | 600 min | Marine-grade heavy load |
4 Finish options
| Finish | Thickness / standard | Salt spray (ref.) | Where it belongs |
|---|---|---|---|
| Electro-galvanized (clear/yellow) | 5–12 μm, ISO 4042 | 48–120 h | Indoor, dry climates — default choice |
| Hot-dip galvanized HDG | 45–85 μm, ISO 10684 / ASTM A153 | 1000+ h | Outdoor structures, coastal inland, decks |
| Zinc-aluminum (Dacromet) | 6–12 μm, Cr-free | 480–1000 h | High salt exposure, automotive |
| Mechanical zinc | ASTM B695 | 300+ h | High strength classes — avoids hydrogen embrittlement |
| Black oxide | — | — | Interior, decorative |
| Stainless plain (A2/A4) | — | per grade | Coast, chemicals, food lines |
Watch the hydrogen trap: carbon steel at 10.9 or Grade 8 is sensitive to hydrogen embrittlement in acid zinc plating. We switch those to mechanical zinc or zinc-aluminum coating and bake them per standard. And if the bolts will sit in treated lumber, plain zinc reacts with the wood tannins — go HDG or stainless there.
5 Recommended tightening torque (reference)
| Size | Stress area As (mm²) | 4.8 class (N·m) | 8.8 class (N·m) | Mating nut |
|---|---|---|---|---|
| M5 | 14.2 | ≈ 3 | ≈ 6 | M5 (ISO 4032) |
| M6 | 20.1 | ≈ 5 | ≈ 11 | M6 |
| M8 | 36.6 | ≈ 13 | ≈ 26 | M8 |
| M10 | 58.0 | ≈ 26 | ≈ 52 | M10 |
| M12 | 84.3 | ≈ 45 | ≈ 91 | M12 |
| M16 | 157 | ≈ 112 | ≈ 225 | M16 |
| M20 | 245 | ≈ 220 | ≈ 439 | M20 |
Based on 70% of yield, friction μ ≈ 0.14, K ≈ 0.20 for zinc. In timber, stop when the square neck seats and the washer just dents the surface — past that point you crush wood fibers. Inch reference: Gr.2 1/2-13 ≈ 40 ft·lb, Gr.5 1/2-13 ≈ 75 ft·lb.
Size Chart & Length Tolerances
| Nominal length L (mm) | 20–33 | 35–50 | 55–80 | 90–120 | 130–150 | 160–180 | 200 |
|---|---|---|---|---|---|---|---|
| Length tolerance (±mm) | 1.05 | 1.25 | 1.5 | 1.75 | 2.0 | 4.0 | 4.6 |
Inch lengths run +.02/-.03 in up to 1 in, widening as length grows. Beyond 200 mm we cut to order — typical lead time quoted at the PO stage.
Applications
Wood decks & pergolas
Deck boards, rail posts, pergola beams. Works with hardwoods like Ipê, Cumaru and Quebracho — just drill the pilot hole at the small end of the range. HDG or stainless finish on anything near the coast.
Fences, corrals & gates
Cercos and potreiros across Argentina, Paraguay and southern Brazil. Post-to-rail joints take M8/M10 or 5/16"-3/8". The dome head keeps livestock from snagging and gives a clean look on the outside.
Farm equipment & agri-machinery
Jigs, guards, wooden tool handles, wagon and trailer boards. Workshops buy 4.8 class in bulk; 8.8 when the joint carries real load. Square neck means one-handed assembly in tight spots.
Timber frames & roofing battens
Timber-to-timber shear connections and roof lath fixing. Pair with a square washer and nut per NDS-style practice. The large bearing area under the head spreads load and stops pull-through.
Playgrounds & public furniture
Park benches, playground frames, bus stops. Smooth heads mean no sharp edges and no rust streaks in public spaces — spec A2 stainless or HDG and the municipality won't call you back.
Metal-to-wood in construction
Steel brackets, angle plates and post bases bolted to timber. The square neck seats into the wood, the nut tightens against the steel side. For steel-to-steel, switch to ribbed neck or hex bolts.
Selection checklist
- Pilot hole: 60–75% of shank diameter in wood; low end for hardwoods.
- Thread stick-out: at least two full threads past the nut.
- Nut grade must match bolt grade — never a weaker nut on a stronger bolt (ISO 898-2).
- Coastal or humid site: HDG or A4-70 stainless. Electro-zinc is for dry interior work.
Why Fasto
We've been making and exporting fasteners for over twenty years. Screws, bolts, nuts, nails, rivets — the whole family, out of our own plant in Hebei. No trading middleman, no "we'll check with the factory" emails. When you ask about a size, finish or tolerance, the guy answering has the drawing on his desk.
Certifications that open doors
IATF 16949 and ISO 9001 cover the plant; CE, SGS and RoHS cover the product. For government tenders and mining supply chains across Chile, Peru and Colombia, that paperwork gets you past the gate.
Full range, both systems
Metric and inch from one line. M5 to M20, #8 to 3/4", plus the short square neck, ribbed and fin neck series. One PO covers your whole carriage bolt assortment — no splitting orders between suppliers.
QC that matches the spec
Go/no-go thread gauges, dimension sampling on dk / k / v / f / b, tensile and proof load tests per ISO 898-1 or ASTM F606, salt spray checks on every coating batch. The square neck gets its own inspection — it's the part that fails if the forming die drifts.
Export packing that survives the trip
Pallets, cartons and steel drums sized for sea freight to Santos, Callao, Buenos Aires or Cartagena. Rust-preventive oil, sealed poly bags, plastic-lined drums for HDG. Bolts arrive as shipped, not as a rusted souvenir.
Pain Points & Solutions
The #1 complaint in every market we ship to. Nine times out of ten the pilot hole was drilled too wide, or the wood is too hard for the neck to bite.
Coastal fog in Lima, humidity in Rio, salt air in Cartagena — plain zinc doesn't stand a chance. We see this daily with cheap electro-plated imports.
Driving a carriage bolt into Ipê or Quebracho without a pilot hole is asking for cracked posts. The square neck also needs a hole it can grip, not a torn one.
Length is measured from under the head, but some buyers measure overall, head included. Result: bolts that sit proud or barely reach the nut. It's the most common error in export POs.
Cheap suppliers blend 4.6 and 4.8 stock, or slap 8.8 marking on soft blanks. A joint that was engineered for one grade gets a bolt of another. Nobody inspects it — until it fails.
Soft zinc threads, damaged plating build-up at the die, or a nut grade below the bolt. Stripped threads on a fence line mean a drill-out job on site.
Container schedules to Santos or Callao plus customs clearance can stretch weeks. A stalled fence contract doesn't wait for a supplier who ships late.
Zinc reacts with tannins in treated and hardwood lumber — the bolt looks corroded even when it isn't. Customers see it and blame the fastener.
From the underside of the head — the root of the square neck — to the tip of the thread. The dome head is not counted. Ordering by overall length is the most common mistake we see in export orders, and it costs a full shipping cycle to fix.
The square neck isn't biting into the base material. Either the pilot hole was drilled too close to full shank diameter, or the base is too hard (steel, dense hardwood). Drill at 60–75% of shank diameter and re-test. For hard steel connections, use a ribbed neck bolt or a hex bolt instead.
Yes, in wood — always. The pilot hole stops the wood from splitting and lets the square neck seat properly. Hardwoods like Ipê, Cumaru or Quebracho need the smaller end of the 60–75% range.
Depends on the climate. Electro-galvanized zinc is fine indoors and in dry regions. For coastal areas, high humidity or salt air, go hot-dip galvanized or stainless (A2-70 / A4-70). Plain zinc will show rust within months in places like Lima, Rio or Cartagena.
Yes, if the square neck can seat into the softer member. For hard steel-to-steel, the neck won't bite and the bolt will spin. In that case pick the ribbed or fin neck series, or switch to a hex bolt.
Depends on size and property class. A common 4.8 class M10 bolt has a minimum tensile strength of 400 MPa — roughly 4,000 kgf on the stress area. For heavy structural loads use 8.8 class and match the nut grade. Never put a lower grade nut on a higher grade bolt.
Q9. Do carriage bolts come with nuts?
They're bolts, so yes — they're made to be used with a hex nut. We supply them with hex nuts (ISO 4032 / DIN 934) and flat washers as a set, or as loose bolts. Tell us your packing preference at the quote stage.