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+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
Type:Stainless Socket Cap Screws
Materials:Stainless Steel
Surface treatment:Plain
Head Type:Cap head (socket)
Drive:Hexagon socket (Allen)
Thread:Machine thread
Point:Plain, chamfered
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10
We make stainless socket cap screws with a tall cap head, a deep hexagon socket and a plain passivated finish, quoting them from M1 to M10 with lengths made to the drawing. The under-head fillet and the socket depth are agreed on the drawing, and the first article is assembled into your counterbore.
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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.
Stainless socket cap screws are cap head screws with a hexagonal socket, made in stainless steel and left plain. The part recorded here is quoted from M1 to M10 with lengths made to the drawing.
Cap head. A tall cylindrical head with a flat bearing face, a deep socket and a fillet where the head meets the shank.
Hexagon socket. An internal hexagon driven from above, sized against the thread diameter.
Stainless body. The alloy carries the corrosion resistance, and cold working during heading and rolling supplies most of the strength.
Machine thread. A uniform thread for a tapped hole, a nut or an insert.
They are used where a joint needs high clamp load and must not corrode: machine frames, pump and valve assemblies, food and pharmaceutical equipment, outdoor fixtures and marine hardware, and any place where a zinc plated cap screw would rust and become impossible to open.
A cap head is designed to bear on its full underside, and that is only possible if the surface it bears on is flat and large enough. In practice the head sits in a counterbore or a spot face, and the diameter of that counterbore is as much a part of the joint as the screw is.
The detail that gets missed is the fillet. Between the head and the shank there is a radius, and it exists because a sharp corner would be a stress raiser and would break in heading. If the counterbore is cut to the head diameter with a square internal corner, the head lands on that radius instead of on its face: the screw feels tight, the joint is not, and the torque has gone into the socket.
That failure is quiet. There is no gap to see, no thread damage, and the assembly looks correct. It shows up later as a joint that loosens, or as a head that has marked the counterbore around a circle slightly larger than the shank. The dimension that prevents it is the counterbore diameter and depth, and it belongs on the mating part’s drawing rather than on the screw’s.
Stainless changes the strength story but not this geometry. A stainless cap screw gets most of its strength from cold working during heading and thread rolling rather than from a heat treatment, so the head and the thread region are stronger than the raw wire, and the fillet is where that working is most concentrated. A joint that loads the fillet instead of the face puts the clamp exactly where the material is least able to spread it.
The socket depth is the other half of the head design. A tall cap head has room for a deep hexagon, which is why it takes more torque than a button head of the same diameter; that depth is what makes a stainless cap screw practical in sizes where the thread alone would not survive the drive.
The recorded range is M1 to M10, with lengths made to the drawing. Custom lengths up to 2,000 mm are subject to the drawing submission and DFM review. The quotation for stainless socket cap screws carries the head diameter and height, the socket size and depth, the thread pitch and the overall length.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Cap head, cylindrical | Diameter, height and face flatness |
| Head fillet | Radius under the head | Radius kept clear of the seat |
| Socket | Hexagon, key size per diameter | Depth and wall thickness |
| Thread | Machine thread in stainless | Pitch, length and start position |
| Length | Overall, head included | Length tolerance and thread start |
| Finish | Plain, passivated | No build; socket as cut |
Head diameter is measured with the fillet radius, because the two together decide how much of the underside can actually bear. A head that is correct in diameter with a fillet that is too generous has less flat area than the drawing implies.
Socket size follows the diameter and the depth follows the head height. On a tall cap head the depth is generous, which is the point of the form; where a lower head is specified for clearance, the socket comes down with it and the torque limit falls.
Length is measured over the head so the datum agrees with the counterbore. On a joint where the head sits in a spot face, the effective thread length is the length minus the counterbore depth, and that is what decides engagement.
Four properties decide stainless socket cap screws, and each one carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Cap head | Deep socket and wide bearing face | Needs a counterbore that clears the fillet |
| Stainless body | Corrosion without a coating | Lower strength than a high-grade steel screw |
| Cold worked strength | Head and thread stronger than the wire | Work-hardens further when driven |
| Plain finish | No layer to wear at the socket | No sacrificial protection at a crevice |
The value is a joint that carries a real clamp load and can be opened years later. That combination is what makes a stainless cap screw worth its price on equipment that is washed, weathered or simply expected to be serviced.
The cost is that everything around the head has to be right. The counterbore, the spot face and the fillet clearance are part of the joint, and a screw that is perfect will still not clamp if the seat it lands on is not flat.
The recorded finish is plain, which on a stainless cap screw means passivated. Passivation removes free iron from the surface and lets the chromium oxide layer rebuild, and on this part it has to reach inside the socket as well as across the head.
| Option | How it protects | Effect on head and socket | Typical use |
|---|---|---|---|
| Passivated, plain | Removes free iron; rebuilds oxide | No build; socket as cut | Default for stainless |
| Electropolished | Levels the surface | Socket edges rounded slightly | Food, medical, cleanroom |
| Black oxide on stainless | Colours the surface | Thin film; key fit unchanged | Dark equipment |
| Vibratory polished | Mechanical smoothing | Edges softened; tone even | Visible fixings |
| Nickel plated | Hard bright barrier | Build in socket; re-gauged | Where a bright finish is wanted |
The socket is where passivation is easiest to get wrong on a cap head. It is deep, narrow and full of internal corners, and free iron from broaching collects there. A batch that is passivated only on the outside rusts first at the point the key bears, which is the worst place for a visible stain.
Where plating is used instead, the socket is gauged after plating. A stainless cap screw has a deep socket to give, but a coating that changes which key seats still changes the torque the joint receives.
Three settings where a high clamp load and a corrosion-resistant body are both needed:
| Where it sits | The screw pulls a frame member or a guard down onto a spot face where the joint must stay tight under vibration. |
| When it goes wrong | The head lands on a square corner in the counterbore and the joint never reaches its clamp load. |
| Why it happens | The parts are heavy, the joint is repeated, and the assembly is inspected. |
| What we control | Fillet and counterbore clearance checked; first article assembled and torque recorded. |
| Where it sits | The screw closes a panel on a machine that is washed down and inspected, where a coating would be a contamination risk. |
| When it goes wrong | A plated screw loses its layer at the socket and corrosion starts where the key bears. |
| Why it happens | The joint is cleaned daily, the fixing is visible, and hygiene is audited. |
| What we control | Passivation verified on the batch; electropolished option offered where specified. |
| Where it sits | The screw holds hardware that will be opened after years of weather and salt air. |
| When it goes wrong | A zinc plated cap screw seizes and the head has to be destroyed to open the joint. |
| Why it happens | The joint is exposed, the fixing is large, and maintenance is infrequent. |
| What we control | Molybdenum-bearing grade specified; salt-spray sample checked before the batch. |
Four reasons that matter on a part whose clamp depends on what it sits on, each tied to something the drawing has to prove:
|
Fillet and socket agreed on the drawing
The head diameter, the fillet radius and the socket depth are confirmed before quoting, because a head that lands on its fillet never delivers the clamp the drawing assumes. Basis: Fillet and socket on the drawing. |
Headed, broached, threaded, passivated
The head and hexagon are formed, the thread rolled, and the batch passivated after forming so both the face and the socket keep their geometry. Basis: One route from wire to passivated screw. |
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Face flatness and socket proved
The bearing face flatness and the socket are measured on every first article, because a face that is not flat loads one side of the socket first. Basis: Face and socket measured. |
Same head, same seat
The heading tool and the broaching punch are recorded with the drawing revision, so a repeat order lands in the same counterbore with the same bearing. Basis: Same bearing across orders. |
These screws are headed on single-die machines that form the cap head and its under-head fillet in one stroke, broached with a hexagonal punch, thread rolled on the stainless shank and passivated as a batch. The first part of every run is measured on head diameter and height, fillet radius, socket size and depth, thread and length.
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The fillet under the head is formed, not machined, so its radius is set by the punch. A punch that is running slightly worn forms a larger radius, and the part still measures correctly on head diameter while its flat bearing area has shrunk. That is why the radius is inspected on the first article and after any tool change.
Stainless is harder to head than carbon steel because it resists flow, so the head is formed with higher pressure and the tooling wears faster. The wear shows first at the fillet and at the rim, and both are measured, because they are the two features the customer’s part touches.
Passivation comes after broaching, and the socket is the area that needs it most. The batch is cleaned, acid treated, rinsed and left to rebuild its oxide layer before packing, and a sample from each lot is checked inside the hexagon rather than only on the head.
What decides whether stainless socket cap screws pass is the head, the socket, the thread and the surface. The inspection agreement covers those, and the criteria come from the drawing.
Fillet and socket on the projector |
Thread and start checked |
Hardness against the stainless spec |
Salt-spray testing of the passivated socket |
Head diameter, height, fillet radius and bearing face flatness are measured on the projector as one set, because the usable bearing area is what results from all four. The socket is measured and proved with the production key, and the thread is gauged after rolling.
Corrosion is checked where it would show first. A sample from each batch goes into the salt-spray chamber, and the socket and the fillet are examined for rust, since those are the two places that hold contamination after forming.
A sample from every batch is assembled into the customer part at the line torque and removed. That cycle shows a head that lands on its fillet, a face that is not flat, or a socket that has begun to mark, and it is recorded with the batch.
Every batch is traceable to the heat of stainless it was made from. The grade and heat number appear 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 shipment we supply the material certificate, the inspection record for the dimensions on the drawing including the fillet radius and socket depth, and the passivation records for the batch. The documents carry the drawing revision and the batch number, so a repeat order of stainless socket cap screws matches the original.
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 cap head the first article is assembled into the counterbore, because the bearing face only proves itself on the seat. 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 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 |
A cap head bears on its flat underside. A counterbore or spot face gives it a flat seat large enough to take the clamp without marking the part.
The head lands on its under-head fillet instead of its face. The screw feels tight and the joint is not.
Most of the strength comes from cold working during forming. A stainless cap screw is usually weaker than a high-grade steel one at the same diameter.
It can, particularly on repeated assembly. Where the joint is opened often, an assembly lubricant or a different material pair is agreed.
The general-purpose austenitic grade for indoor and dry joints, and the molybdenum-bearing grade for chlorides, wash-down and coastal air.
Head diameter and height, fillet radius, socket size and depth, thread pitch and overall length.
How a stainless socket cap screw project runs from drawing to repeat delivery:
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1
Send the drawing and the counterbore size
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→ |
2
Fillet clearance and socket agreed
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→ |
3
First article assembled in your counterbore
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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 head diameter and height, socket size and depth, thread pitch and overall length.
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Head diameter
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Head height
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Socket size
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Socket depth
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Thread pitch
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Length
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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
