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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:Flat Head Security Screw
Materials:carbon steel
Surface treatment:nickel plated
Head Type:flat head
Drive:Internal Triangle
Thread:Machine Thread
Point:Blunt
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:402
We make flat head security screws in nickel plated carbon steel with a countersunk head, an internal triangle socket and a machine thread, quoting them from M1 to M14. Cone, socket, thread and plating come from your drawing, and the first article is seated in your countersink and turned with your key.
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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.
A flat head security screw is a countersunk screw with a recess that an ordinary screwdriver will not turn, so the fixing sits flush and cannot be undone with what is in a pocket. The recorded item on this page is nickel plated carbon steel with a countersunk head, an internal triangle socket and a machine thread, quoted from M1 to M14 with Number 402.
Countersunk head. A cone that seats in a matching countersink and leaves the surface unbroken. It centres the screw as it is turned and bears on the cone rather than on a face, which is what makes the joint flush.
Internal triangle socket. A three-sided recess with three flat faces, driven with a triangular key. It takes no common bit, and it seats on all three faces rather than tipping on a corner.
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, so a security screw of this type protects against casual access rather than sealing the joint for good.
Nickel plated carbon steel. A hard, bright barrier deposit over a steel body that is itself harder than stainless. That combination is chosen for the recess, not for the looks: the socket has less material than a cross and it wears better on a hard base metal.
On flat head security screws the base metal matters more than on an ordinary screw. A triangular socket has three corners and three faces, and the corners are the smallest features in the head; every drive wears them a little. Carbon steel, hardened, holds those corners far better than an annealed stainless, which is why a flat head security screw in a dry indoor assembly is often steel with a coating rather than stainless.
That choice has a cost, and it is the coating. Nickel protects by keeping the atmosphere off the steel, not by corroding in its place, so once the deposit is broken the steel at that patch rusts. In a wet or washed joint the base metal, not the coating, decides the outcome, and stainless is the right answer there — with the softer socket that comes with it.
On flat head security screws the countersunk cone is the second structural feature. It seats on a matching countersink cut into the part, and the cone carries the clamp load over its whole area. On thin sheet the material around the countersink is the weakest part of the joint, and it deforms before the screw does; a triangular key cannot deliver enough torque to do that quickly, which is a useful match.
The socket is formed in the heading stroke and its depth is limited by the head height. On a countersunk head the material above the cone is thin, so the socket is shallower than on a pan head — one more reason the drive suits a joint with a low torque requirement.
Nickel is plated after the thread is rolled and the socket is formed. It builds a few microns inside the socket, which on a triangle narrows the faces and makes the key sit high; the socket is tried with the production key in the plated condition on the first article of every batch.
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 flat head security screws the cone angle, the socket size and the thread length are quoted together, because all three decide whether the joint closes and stays closed.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Countersunk cone, flat top | Cone angle, diameter and concentricity |
| Socket | Internal triangle, three faces | Across corners, depth, key tried after plating |
| Thread | Machine thread | Pitch and length, gauged per batch |
| End | Blunt, chamfered | Chamfer cut, not deburred |
| Plating | Nickel, bright | Thickness range and socket clearance |
| Length | From the top of the head to the end | Measured on the shop plate |
The cone angle is quoted against the countersink the customer cuts. Ninety degrees is the common case; a head a degree out seats on a line, looks flush from above and rocks when pressed. The first article is seated in a sample of the customer’s panel for that reason, not judged against a drawing.
Length is measured from the top of the head, because a countersunk head finishes flush and the top face is the datum that shows. Measuring from the start of the cone instead gives a screw that is short by the head depth, and in a thin panel that difference is the entire thread engagement.
Three features define this part: the countersunk head, the triangular socket and the nickel over carbon steel. The first gives a flush joint, the second limits who can open it, and the third is a deliberate choice of hardness over corrosion.
| Feature | What it gives | What it costs |
|---|---|---|
| Countersunk head | Flush surface, self-centring | Bears on thin sheet, which is the weak point |
| Triangle socket | No common bit will turn it | A key is needed for service; low torque ceiling |
| Carbon steel base | Hard corners that survive repeated driving | Rusts at a scratch through the plating |
| Nickel plate | Bright, hard, even on a visible cone | A few microns narrow the socket |
| Machine thread | Removable, serviceable | Needs a tapped hole or a nut |
The pairing of a low-torque drive with a head that cannot safely take high torque is the clean part of the design. A countersink in thin sheet should not be over-driven, and a triangular key cannot over-drive it. What the pairing does not fix is the socket wear: a security screw that is opened many times rounds its triangle, and on a nickel plated part the damage shows as bright metal on all three corners at once.
Nickel plating is also what makes the part presentable. The cone is the largest visible surface on a flush fixing, and a bright even deposit hides tool marks better than a zinc or oxide finish, which is why security screws on visible black or chrome equipment are often nickel plated regardless of the base metal.
The recorded finish is bright nickel over carbon steel. It is a barrier coating: it protects as long as the film is intact, and where it is broken the steel below is exposed and rusts at that point rather than around it.
| Option | How it protects | Effect on cone and socket | Typical use |
|---|---|---|---|
| Nickel plated steel | Hard barrier deposit | A few microns; key tried after plating | Dry indoor equipment |
| Stainless A2, plain | Passive chromium oxide film | None; gauged as formed | Outdoor and washed |
| Stainless A4, plain | Passive film with molybdenum | None; gauged as formed | Chloride and marine |
| Zinc plated steel | Sacrificial zinc | A few microns; socket re-checked | Cost-driven indoor work |
| Black zinc on steel | Sacrificial zinc, dark passivation | A few microns; socket re-checked | Dark visible panels |
The choice between nickel plated steel and stainless is not about price alone. On a joint that is opened repeatedly in a dry place, the harder base metal keeps the socket usable for longer; on a joint that sees water, the austenitic alloy keeps the part intact for longer even though its socket wears sooner. The two answers are correct for different services, and the drawing should name one rather than say security screw.
Where a nickel plated part is used in a damp joint anyway, the failure starts inside the socket: water sits in the triangle, air is excluded, and the plated corner rusts first. That is why the same screw in the same panel behaves differently depending on whether the panel is under a cover or exposed to a wash.
Three assemblies where a flat head security screw is the fixing:
| Where it sits | The screw closes a cover over terminals or a board where the surface has to be flush, access should be restricted, and the panel is indoors and dry. |
| When it goes wrong | A flush head that rocks breaks the seal or the paint at the cone, and a standard drive invites access to live parts. |
| Why it happens | The cover is flush, the fixing repeats, and the environment is dry. |
| What we control | Cone and socket checked, key tried on the first article, plating thickness held. |
| Where it sits | The screw fixes a plate on equipment that is unattended and serviced by staff with a key, where the fixing must not stand proud. |
| When it goes wrong | A proud head is a lever for tampering and a snag for the public; a common drive makes the plate a target. |
| Why it happens | The equipment is unattended, the surface is public-facing, and the fixing is serviced. |
| What we control | Socket across corners checked, thread gauged, cone seated in a sample panel. |
| Where it sits | The screw closes a panel where the manufacturer wants the case opened only by service and the head sits flush in a visible face. |
| When it goes wrong | A bright head standing proud marks the design, and a rounded socket ends the repair. |
| Why it happens | The housing is visible, the joint is serviced, and the fixing repeats. |
| What we control | Plating tone held to the sample, socket and thread checked. |
Four reasons that matter on a countersunk security screw, each tied to what the drawing has to prove:
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Cone, socket and base metal reviewed together
The cone angle, the socket size and the choice of carbon steel or stainless are reviewed as one set, so a head that would rock or a socket that would wear is raised before the die is cut. Basis: Cone, socket and base metal reviewed as one set. |
Heading, rolling and plating in one route
The countersunk head and the triangular socket are formed in one stroke, the thread is rolled and the parts are nickel plated and baked in one route. Basis: One route from wire to plated screw. |
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Key tried in the plated socket
The socket is checked across corners and for depth, then driven with the production key in the plated condition on the first article. Basis: First article turned with the production key. |
First article fixes the setting
The first article fixes the wire heat, the socket punch, the roll and the plating barrel; repeat orders are compared against that record. Basis: First article signed off before the batch is released. |
Shi Shi Tong forms these flat head security screws from carbon steel wire on single-die headers that cut the countersunk cone and the triangular socket in one stroke, rolls the machine thread to a blunt chamfered end, nickel plates the parts and bakes them. The first part of every run is measured on the cone, turned with the production key and run into a threaded sample before the batch continues.
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The socket punch wears at the three corners, and on a countersunk head it has less material around it than a pan head would. A worn punch leaves a socket wider at the mouth than at the floor, so the key sits high and the torque goes into the corners — the one place a flush security head cannot afford to lose material. The socket is checked with the key on the first article and sampled through the run.
What decides whether flat head security screws pass is the cone, the socket, the thread and the plating. The inspection agreement covers those, and the criteria come from the drawing.
Cone and socket on the projector |
Thread gauged after plating |
Hardness checked against the property class |
Salt-spray testing of the nickel plate |
The cone is checked for angle, diameter and concentricity, and the socket across corners and for depth. Both are then proved in use: the first article is seated in a countersunk sample and turned with the production key, because a cone that measures right can still seat on a line and a socket that measures right can still refuse a key.
Seating is checked with a light behind the head, which is the customer’s acceptance test on a flush joint. Plating thickness is measured on the sample and the socket is re-checked after it, since a few microns is a real fraction of a triangle that is already small.
Every shipment of flat head security screws is traceable to the wire it was made from and to the plating 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 material or the plating. 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 a security screw the first article is also the point at which the key is agreed, so the customer confirms the tool at the same time as the screw. Buyers visit during the process to review samples and to see how the heads and sockets are formed.
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8,678+
customers served
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87%
of orders from repeat customers
|
56%
of orders through referrals
|
89
countries and regions shipped to
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Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the headers and the plating 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 |
An internal triangle: three flat faces driven with a triangular key. It takes no common bit and seats on all three faces rather than on a corner.
Carbon steel is harder, so the three corners of the socket last longer. Nickel over it is fine indoors; in a wet joint stainless is the right base metal despite the softer socket.
A few microns narrows it measurably. The socket is tried with the production key after plating, on every batch.
That is what the countersunk cone is for. A head that sits proud is a snag and a lever; a cone that does not match its countersink looks flush and rocks.
With the key, yes. The triangle wears at its three corners, so a joint that is opened often should use a standard drive instead.
Cone angle and diameter, socket across corners and depth, thread size and length with the datum, length from the top of the head, and the finish.
How a flat head security screw project runs from drawing to repeat delivery:
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1
Send the drawing and the countersink sample
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→ |
2
Cone, socket and thread review
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→ |
3
First article seated and turned with the key
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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 cone angle and head diameter, the socket across corners and depth, the thread size and length with the datum, the length from the top of the head, and the finish.
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Cone angle
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Head diameter
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Across corners
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Socket depth
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Thread and datum
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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
