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+86 13143444311
Email：sst@szsst88.com
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Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Type:Corrosion Resistant Screws
Materials:stainless steel
Surface treatment:plain
Head Type:hex head
Drive:Hex Head
Thread:Machine Thread
Point:Blunt
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:604
We make corrosion resistant screws in A2 and A4 stainless with a hex head and a machine thread, passivated so the surface is the alloy rather than a coating. Grade, head, thread and passivation come from your drawing, and the joint materials are reviewed with the grade so the screw does not corrode its neighbour.
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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.
Corrosion resistant screws are fasteners whose resistance comes from the alloy rather than from a coating, which is what lets them survive weather, washing and chemical exposure without a finish to maintain. The recorded item is stainless steel with a plain finish, a hex head and a machine thread, quoted from M1 to M14 with Number 604.
Stainless body. A chromium-bearing alloy protected by a passive oxide film a few nanometres thick. The film reforms when it is scratched, which is the property that makes this family different from anything plated.
Hex head. Six flats driven with a spanner or a socket, with no recess in the top. The head is shallow for its diameter and the drive is the outside of it.
Machine thread. A rolled thread with a blunt chamfered end, made for a tapped hole or a nut. It comes out and goes back in without damaging the thread in the part.
Plain finish. Passivated and uncoated. A coating on a corrosion resistant screw usually does more harm than good, because it hides the alloy and can trap water at its edges.
A plated screw resists corrosion by being covered; a corrosion resistant screw resists it by being the right metal. The chromium in the alloy combines with oxygen to form a film that is a few nanometres thick, tightly bound and self-healing: scratch it and the film rebuilds in air within minutes, as long as there is oxygen and no contamination.
On corrosion resistant screws that has a consequence for how the part is specified. There is no coating thickness to quote, so the drawing quotes a grade instead, and the grade is the entire corrosion specification. Two screws of the same size and finish can differ by a factor in service life purely on whether one is a 304 and the other a 316.
On corrosion resistant screws the film also explains the failure modes. It needs oxygen, so where oxygen is excluded — under a washer, inside a crevice, in a thread that is never opened — the film can break down and not rebuild. That is crevice corrosion, and it is the reason a joint can fail halfway through even though the exposed head looks perfect.
The hex head and machine thread are the practical part of the design. A hex is driven with a spanner, so there is no recess to fill with water or debris, and the head is shallow enough to sit under a washer or in a counterbore without a pocket. On a joint that is cleaned often, a recess is a place water sits.
Passivation after forming is what restores the film on the finished part. It removes free iron left by the tools and rebuilds the oxide; without it a stainless screw can show rust spots that come from tooling contamination and are read, wrongly, as a material failure.
The family is quoted from M1 to M14, with M1, M2, M3, M4, M5, M6, M7, M8, M9, M10 and M14 in the recorded range. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission; on corrosion resistant screws the grade is quoted with the head and thread, because the grade is the specification that matters most.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Hex head, six flats | Across flats, height and face squareness |
| Thread | Machine thread | Pitch and length, gauged per batch |
| End | Blunt, chamfered | Chamfer cut, not deburred |
| Grade | A2, A4 or a grade named on the drawing | Confirmed on the material certificate |
| Finish | Plain, passivated | Surface condition and passivation |
| Length | From under the head to the end | Measured on the shop plate |
Across flats is a handling dimension and it is quoted with the grade. A stainless hex that is under size still looks like a hex, and a spanner that is loose on it rounds the corners on the first pull; because there is no plating to hide the damage, the mark shows immediately.
Length is measured from under the head, because that face bears. On a hex head the head height adds to the overall length, so a screw quoted into a counterbore has to allow for it or the face will never touch the part.
Three features define corrosion resistant screws — the stainless body, the hex head and the machine thread — and the body is the one that decides the service life. Stainless is not a single answer to corrosion; it is a family, and each member has a limit.
| Attack | What happens | Where it bites | What prevents it |
|---|---|---|---|
| Pitting | Chloride breaks the film locally | Coastal and chlorinated service | Molybdenum — A4 rather than A2 |
| Crevice | Oxygen is excluded, the film cannot rebuild | Under washers, inside threads | Seal the joint or open the crevice |
| Galvanic | A more noble partner drives corrosion | Stainless against aluminium | Isolate the joint |
| General | The alloy is simply the wrong one | Hot concentrated acids | A different grade, not a coating |
Pitting is the failure that surprises customers, because it happens in a material chosen to prevent it. A2 handles most inland weather; in a coastal atmosphere the chlorides break the film down at the weakest points, which are usually the cut edge of a thread and any inclusion at the surface, and the pit then grows inward. A4 with molybdenum resists that longer, and even A4 has a limit in hot concentrated chloride.
The galvanic case is worth stating because it damages the other part. Stainless is a noble metal in the galvanic series, so in a wet joint it drives corrosion of whatever is less noble that it touches — aluminium, carbon steel, or a plated fastener. The stainless screw survives and the aluminium panel around it does not, which is a failure customers rarely blame on the screw.
Corrosion resistant screws are finished plain and passivated. Nothing is added, so the thread, the hex and the chamfers are exactly as formed, and the protection is the alloy rather than a film that can be scratched off.
| Option | How it protects | Effect on thread and head | Typical use |
|---|---|---|---|
| A2 plain, passivated | Passive chromium oxide film | None; gauged as formed | General outdoor and indoor |
| A4 plain, passivated | Passive film with molybdenum | None; gauged as formed | Coastal, pool and chemical |
| PTFE coated | Dry film barrier plus lubricant | Film builds; thread re-checked | Seizing joints, food equipment |
| Zinc plated steel | Sacrificial zinc | A few microns; re-checked | Indoor, cost-driven work |
| Dacromet on steel | Zinc-aluminium flake layer | Film builds; thread re-checked | Outdoor steel structures |
Coating a stainless screw is usually a mistake. The coating is a barrier where the alloy was already a better barrier, and it introduces an edge at which water can sit, so a coated stainless part can corrode at the coating boundary where a plain one would not. The exceptions are lubricating finishes — a dry film that stops galling — and cases where a colour is required.
Where a dark tone is wanted, the answer is a black oxide or a black coating applied with the alloy’s behaviour in mind, and the drawing says which. What should not happen is a stainless part being plated simply because the rest of the batch is.
Three assemblies where corrosion resistant screws are the fixing:
| Where it sits | The screw fixes a fitting, a bracket or a panel where salt spray is continuous and the fixing is expected to outlast the finish around it. |
| When it goes wrong | A2 pits at the thread within a season, and a stainless screw against an aluminium part corrodes the panel instead. |
| Why it happens | The service is salt-laden, the joint is exposed, and the parts are replaced individually. |
| What we control | A4 confirmed on the certificate, passivation checked, joint isolated where aluminium is present. |
| Where it sits | The screw holds a guard, a cover or a fitting where the part is washed with detergents or chlorinated water and a coating would trap residue. |
| When it goes wrong | A coating chips into the product area, and a grade that is wrong for the cleaning chemical pits at the crevice under the washer. |
| Why it happens | The joint is cleaned often, the surface is inspected, and the environment is wet. |
| What we control | Grade matched to the cleaning regime, passivation confirmed, crevices minimised. |
| Where it sits | The screw fixes cladding, a handrail or a fitting where the joint sees rain, pollution and temperature cycling for a long service life. |
| When it goes wrong | A plated screw rusts at the head and stains the facade, and a crevice under a washer traps chloride. |
| Why it happens | The joint is exposed, visible, and expensive to revisit. |
| What we control | A2 or A4 by atmosphere, passivation confirmed, washers matched to the screw. |
Four reasons that matter on corrosion resistant screws, each tied to what the drawing has to prove:
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Grade, environment and joint reviewed together
The grade, the atmosphere and the materials it touches are reviewed as one set, so a screw that would pit or a joint that would corrode its neighbour is raised before the batch is made. Basis: Grade, environment and joint reviewed as one set. |
Heading, rolling and passivation in one route
The hex head is formed, the thread is rolled and the parts are passivated in one route, so the film is restored on every surface the tools touched. Basis: One route from wire to passivated screw. |
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Grade proved on the certificate
The alloy is confirmed on the material certificate and, where the drawing calls for it, by a corrosion test, rather than assumed from the appearance. Basis: Grade confirmed on the certificate and salt spray. |
First article fixes the setting
The first article fixes the wire heat, the die set and the passivation; repeat orders are compared against that record. Basis: First article signed off before the batch is released. |
Shi Shi Tong forms these corrosion resistant screws from stainless wire on single-die headers that upset the hex head, rolls the machine thread to a blunt chamfered end and passivates the parts before packing. The first part of every run is measured across the flats, checked for surface condition and entered into a thread gauge before the batch continues.
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Passivation is the step that decides whether the part looks like the grade it is. A stainless screw that has not been passivated can show rust spots from the tooling within a week of packing, and those spots are read by the customer as a material failure even though the alloy is correct. The passivation bath and the rinse are controlled and recorded as part of the batch.
What decides whether corrosion resistant screws pass is the grade, the surface, the head, the thread and the passivation. The inspection agreement covers those, and the criteria come from the drawing.
Across flats and head height on the projector |
Thread gauged per batch |
Hardness checked against the grade |
Salt-spray testing of the grade and passivation |
The grade is confirmed on the certificate, and where the drawing calls for a salt-spray result the sample is kept with the batch. Appearance is not evidence: two grades look identical on the bench, and the difference only shows after weeks in a chloride atmosphere.
The head of a corrosion resistant screw is checked across flats and for squareness, and the thread is gauged per batch. On a plain stainless part every mark is visible, so the surface is inspected for tool marks, scratches and any rust bloom that would indicate free iron left by the tools.
Every shipment of corrosion resistant screws is traceable to the wire it was made from and to the passivation batch. The grade and heat number are recorded on the material certificate supplied with the parts, and the inspection records follow the criteria agreed on the drawing.
ISO 9001:2015 |
RoHS test report |
Registered trademark |
Patent: security screw and driver |
With each batch we supply the material certificate, the inspection record for the criteria on the drawing and, where it is listed, the third-party report for the grade or the passivation. The documents carry the drawing revision and the batch number, so the paperwork can be matched to the parts.
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 corrosion resistant screws the first article is also the surface sample, since the finish is the alloy and a contaminated batch cannot be fixed after the fact. Buyers visit during the process to review samples and to see how the parts are formed and passivated.
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8,678+
customers served
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87%
of orders from repeat customers
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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 headers 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 |
No. It is resistant within limits set by the grade: A2 handles weather, A4 handles chloride, and neither handles hot concentrated acids. The grade is the specification.
The film needs oxygen to rebuild. In a crevice — under a washer, inside a thread — oxygen is excluded and the film breaks down, so the part fails where nobody can see it.
Stainless is noble in the galvanic series. In a wet joint it drives corrosion of the less noble metal it touches, so the screw survives and the panel does not.
Usually not. The alloy is a better barrier than the coating, and the coating edge can trap water. Coat only for lubricity or colour, and say so on the drawing.
It removes free iron left by the tools and rebuilds the oxide film, so the part does not show rust spots that come from the tooling rather than the metal.
Hex across flats and head height, thread size and length, the stainless grade, passivation, and any joint material that must be isolated from the screw.
How a corrosion resistant screw project runs from drawing to repeat delivery:
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1
Send the drawing and the service conditions
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→ |
2
Grade, joint and thread review
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→ |
3
First article checked and passivated
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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 from the first article is what repeat orders are checked against.
For a quotation, send the drawing with the hex across flats and head height, the thread size and length, the stainless grade, the passivation requirement and the materials the joint touches.
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Across flats
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Head height
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Thread and length
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Stainless grade
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Passivation
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Joint materials
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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
