Tel：
+86 13143444311
Email：sst@szsst88.com
Fax：+0086-755-27322278
Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Place of Rorigin:Guangdong, China (Mainland)
Brand name:OEM
Model number:sst 3
Materials:Stainless steel
Surface treatment:Cleaned and passivated
Head Type:Domed head, no recess
Neck:Square neck under the head
Thread:machine thread
Point:Plain, chamfered
Forming:Cold heading; head and neck formed together; thread rolled
Size:M8*22
Available materials:titanium, aluminum, copper, stainless steel, carbon steel
process:single mold
We make stainless carriage bolts with a smooth domed head and a square neck, quoted with the neck size, head form and thread to the timber they enter. The square neck is what makes the fixing a one-person job: it bites into the material and holds the bolt while the nut is turned on the far side.
Watch the factory video·Email sst@szsst88.com
ISO 9001:2015 · Manufacturing since 1998 · 8,678+ customers · 89 countries and regions
Made to order – there is no stock catalogue. Each part is produced to your drawing, and production starts after drawing review and first-article approval.
A carriage bolt has a smooth domed head, a square neck just under it, and a thread at the far end with no slot or socket on the head. This one is stainless steel, M8 by 22 in the sample, cleaned and passivated, with a truss-shaped head.
Domed head. A smooth dome with no recess, so there is nothing to drive from the head end.
Square neck. A short square section that presses into the material and stops the bolt rotating.
Thread at the end. Enough thread for a nut and washer, with a plain shank behind it.
Stainless body. No coating, and no rust at a joint that is often outdoors.
A carriage bolt is used in timber, board and composite assemblies where the head must stay smooth on the outside face and the nut is reached from the other side of the material, usually from underneath the deck or the frame.
The whole point of a carriage bolt is the square neck. When the bolt is drawn into its hole, the corners of the square bite into the material, and the bolt can no longer turn. That means one person, one spanner, and a nut that can be tightened from the far side without anything holding the head.
No other common fastener does that. A carriage bolt has no drive on the head at all, so the neck is not a convenience but the mechanism: with a round neck it would spin in the hole and the joint could never be made.
That is also why a carriage bolt is a timber fastener rather than a general one. Softwood and board deform around the square and grip it; steel does not, and a carriage bolt in a round steel hole simply turns. Where the material is metal, a hex bolt or a socket head is the right choice instead.
The neck sets a minimum material thickness as well. A square neck needs enough depth to bury itself, so a carriage bolt in very thin sheet has nothing to bite and behaves like a smooth shank. On thin material the answer is a different fastener.
The domed head finishes the joint. It has no recess, so nothing collects, nothing rusts at a slot, and there is no way to grip it from outside. That is the reason carriage bolts are used on gates, decks and benches where the fixing is exposed.
So a carriage bolt is specified by the material it enters and the square neck that has to bury in it, not by a torque value. The thread only takes the nut, and the head only finishes the face.
Carriage bolts are quoted by head diameter and height, neck size and length, shank diameter, thread size and pitch, threaded length, and finish. Custom lengths up to 2,000 mm, subject to DFM review after drawing submission. The quotation carries the material, the head, the neck, the thread and the finish.
| Item | How it is defined | What we control |
|---|---|---|
| Body | Stainless steel | Grade and mechanical properties |
| Head | Domed, smooth | Diameter, height and face |
| Neck | Square section | Size, height and corner radius |
| Shank | Plain length | Diameter and roundness |
| Thread | At the end | Size, pitch and length |
| Finish | Cleaned, passivated | Surface condition and burr |
The neck size is the dimension to write. It is what presses into the material, and a neck that is a little large splits a board while one that is small does not grip. On a carriage bolt the neck is the working feature, not the thread.
The head is written for the face it finishes. A truss-shaped dome sits close to the surface and spreads load, which is why carriage bolts are usually made with that form.
The threaded length is written for the nut and washer. A carriage bolt with too little thread cannot draw the joint up; too much and the thread runs under the material and wears the hole.
Four properties decide this part, and each carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Square neck | A bolt that holds itself while the nut turns | It needs a deformable material to bite |
| Smooth head | A clean face with no recess | Nothing to drive or grip from the head |
| Thread at the end | A nut and washer on the far side | One face has to stay accessible |
| Stainless body | No rust on exposed timber joints | Galls in a stainless nut |
The value is a single-part fixing that one person can install from one side of a timber assembly, with a head that nothing catches on and that nothing collects in over the years of use.
The cost is that it only works in material soft enough to take the square neck, and that the far side of the joint has to be reachable for the nut and washer.
The recorded finish is cleaned and passivated stainless. On a carriage bolt that matters because the joint is usually outdoors: there is no plating to chip at the neck, and the head stays bright instead of rusting where hands and weather reach it.
| Option | How it protects | Effect on the neck | Typical use |
|---|---|---|---|
| Plain stainless | Natural oxide | No build; neck as cut | Decks, gates and benches |
| Passivated | Clean, thickened oxide | No build; free of free iron | Marine and coastal timber |
| Hot dip galvanised | Thick zinc layer | Builds; neck re-checked | Structural timber outdoors |
| Zinc plated | Thin sacrificial layer | Thin; neck as cut | Indoor board assemblies |
| Black oxide | Conversion layer | Thin, matte | Decorative dark timber |
On a carriage bolt the finish is also a fit question: a thick coating on the square neck makes the neck larger, and a neck that was correct bare can split the board when it is coated. Hot dip galvanised carriage bolts are checked on the neck before approval.
Where the timber is damp and the bolt is stainless, the interface with a steel washer is worth a thought: a stainless carriage bolt against a galvanised washer is a galvanic pair, and the smaller area corrodes.
Three products where one person has to fix from one side:
| Where it sits | The bolt passes through a plank and a joist, and the nut is reached from below. |
| When it goes wrong | The bolt spins in the plank and the nut will not tighten, or the head sinks. |
| Why it happens | The square neck is too shallow for the plank, or the hole is too large. |
| What we control | Neck size and height set from the plank; first article driven and tightened. |
| Where it sits | The bolt holds a rail where the head is visible on the outside face. |
| When it goes wrong | The head rusts, or the joint loosens and the rail moves. |
| Why it happens | The grade is not suited to weather, and the nut has no washer under it. |
| What we control | Grade and washer agreed; sample exposed and inspected. |
| Where it sits | The bolt joins boards that are seen from both sides. |
| When it goes wrong | The head marks the board, or the neck splits the timber. |
| Why it happens | The head is small for the board, and the neck is a tight fit in a dry hole. |
| What we control | Head diameter and neck fit agreed; sample assembled and checked. |
Four points that decide whether a carriage bolt grips and finishes the way it should:
|
Neck written as a dimension
The drawing gives the neck size and height, because the square is what stops rotation and what splits a board. Basis: Grip and fit controlled. |
Head and neck formed together
The neck is formed in the heading tool, so it runs true to the shank and presses evenly into the timber. Basis: Neck square to the shank. |
|
Driven into real timber
The first article is driven into a sample of the customer timber and the nut run down without holding the head. Basis: One-person assembly proved. |
Same neck every lot
Neck size, head form and coating are recorded with the drawing revision, so a repeat lot bites the same. Basis: Same fit across lots. |
A carriage bolt that is a hundredth over on the neck will split a dry board; one under will spin. These four points are what turns that narrow window into something a repeat order can hit.
These bolts are cold headed from stainless wire, with the dome formed and the square neck struck in the same operation, the thread rolled on the end, and the parts cleaned and passivated. The first piece of every run is measured on head, neck, shank, thread and length.
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The neck is formed by the header tool, and its corners are what do the work. A tool that is slightly worn leaves rounded corners, and a carriage bolt with rounded corners slides rather than bites, which shows up as a joint that never tightens.
The head is formed in the same blow, so a carriage bolt is cheap to make and hard to correct afterwards. The dome cannot be machined back without losing the transition to the neck, so the tool is the specification.
Stainless work-hardens at the thread, and the thread is rolled rather than cut where the size allows, which leaves the crest harder and reduces the chance of galling in the nut.
What decides whether a batch of carriage bolts passes is the neck that bites, the head that finishes the face and the thread that takes the nut. The inspection agreement covers all three.
Head and neck on the projector |
Thread checked with gauges |
Material checked |
Salt-spray testing where required |
The neck is measured for across-corners and height and inspected for sharp, square corners. A carriage bolt with rounded corners passes a dimensional check and fails in the timber, so the corner form is judged on the projector and by driving a sample.
The head is measured for diameter and height and checked for a continuous dome. A dome with a flat spot shows on a painted gate as a bright patch where the paint rubs.
The thread is gauged and a nut run down by hand. A carriage bolt is installed with one spanner, so a thread that needs force to start defeats the purpose of the square neck.
Every batch of carriage bolts is traceable to the wire it was made from. The material certificate states the grade, the heat number, the chemistry and the mechanical properties, and the inspection record carries the head, neck, thread and length against the drawing.
ISO 9001:2015 |
RoHS test report |
Registered trademark |
Patent: security screw and driver |
With each shipment we supply the material certificate and the inspection record for the head, neck and thread. The records carry the batch number, so a repeat order can be compared with the first on the neck size that decides whether the bolt grips or splits the timber.
More than 8,678 customers in 89 countries and regions have ordered from Shi Shi Tong; 87% of orders come from repeat customers and 56% through referrals. Most projects follow the same route: drawing review, first-article approval, then batches checked against that sample. On a carriage bolt the first article is driven into the customer’s timber, because the neck is a fit against the material and nothing else. Buyers visit during the process to review samples.
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8,678+
customers served
|
87%
of orders from repeat customers
|
56%
of orders through referrals
|
89
countries and regions shipped to
|
Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the heading cells and the passivation line can be seen on the day the parts run.
Customer group visit – sample review |
Customer group visit – process discussion |
Customer group visit – factory tour |
Customer visit – project kick-off |
Danish customer – drawing review |
Industry exhibition – meeting customers |
The head is not meant to be driven. The square neck holds the bolt while the nut is turned on the far side.
It bites into the timber and stops the bolt rotating, so one person can tighten the joint with one spanner.
Only with a square hole. In a round steel hole the neck has nothing to bite and the bolt turns.
Deep enough for the neck to bury itself. In very thin sheet the square does nothing.
Rounded corners slide instead of biting, and the joint never tightens.
Head size, neck size and height, shank, thread, length, finish, the material it enters and the thickness of that material.
How a carriage bolt project runs from drawing to repeat delivery:
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1
Send the drawing and a timber sample
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→ |
2
Neck, head and thread agreed
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→ |
3
First article driven and tightened
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→ |
4
Batch production and repeat orders
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Each step is confirmed with you before the next one starts; the drawing revision used for the first article is what repeat orders are checked against.
For a quotation, send the drawing with the head diameter and height, neck size and height, shank, thread, length, finish and the material the neck enters.
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Head
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Neck
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Shank
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Thread
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Length
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Finish
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Sending a drawing? The form below does not take attachments. Email the PDF, DXF or STEP file to sst@szsst88.com with the part name and quantity in the subject line – the drawing is reviewed and a quotation follows.
+86 13143444311
sst@szsst88.com
