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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:Tamper proof machine screw (security recess)
Materials:Stainless steel 304
Surface treatment:Passivated
Head Type:Pan head / binding head
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Drive:Security recess, pin style (four-lobe with pin)
Thread:Machine thread, right hand
Forming:Single-die cold heading with formed security recess; thread rolled, then passivated
Number:891
We manufacture tamper proof machine screws in stainless 304 with a pan head and a pin-style security recess, quoted from M1 to M14, single-die headed and passivated. Recess type, pin position, thread and the service bit are settled from your drawing.
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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 tamper proof machine screw is a machine screw whose drive is designed so that an ordinary screwdriver, or an ordinary bit, cannot turn it. The recorded item on this page is a stainless 304 screw with a pan head and a pin-style security recess, quoted from M1 to M14, supplied passivated with a machine thread.
Security recess. The drive is not a standard cross or hexagon. Depending on the drawing it can be a pin in the centre of the recess, a one-way slot that only turns in one direction, a four-lobe recess with a pin, or a spanner-style two-hole head. Each needs a matching tool, and most of them are not in a general toolkit.
Deterrence, not a lock. A security screw does not make a joint unopenable; it makes casual opening inconvenient, and it makes opening visible because the tool marks the head. That is the honest way to specify it: the part is chosen to keep a panel closed against opportunity, not against a determined attack.
Machine thread. The thread is a standard machine thread that engages a tapped hole or a nut, so the security is in the drive, not in the body. That means a security machine screw can be used on any joint that already accepts a normal machine screw of the same size.
Pan head. A low dome with a flat bearing face, wide enough to spread the clamp load on a thin panel and to cover the hole. The pin-style recess sits in the centre of the head, where there is enough material to hold it.
Together these decide the part: the recess decides who can open the joint, the pan head covers the panel, the machine thread fits the existing hole, and the stainless body keeps the screw from rusting once the panel is closed. That is why a tamper proof machine screw is specified by drive, head, thread and material together.
The body of this tamper proof machine screw is stainless 304 wire, with the heat number kept with the batch record. 304 is the recorded grade and the sensible default for a screw that will sit on a panel through several service seasons, be rained on, and be removed only when the equipment is serviced.
The pan head and the security recess are formed in one heading operation. The pin, where the design has one, is formed in the die as part of the recess, so it is as hard as the head around it and it cannot be unscrewed on its own the way a pressed insert could.
The machine thread is rolled over the full length. Rolling gives a smooth flank without the burr a cut thread leaves at the end, and it keeps the shank strong in the section between the head and the thread, which is where a security screw is most likely to be over-torqued when someone tries to force it.
The parts are passivated after forming. Passivation removes free iron from the surface and restores the chromium oxide film, so the screw stays stainless in service and there is no coating to chip out of the recess and leave a bright spot that advertises the joint has been opened.
There is no coating on the recess for the same reason. A plated recess that has been turned a few times shows the marks immediately, which is useful for the owner but bad for the appearance; a plain passivated head shows marks too, but it does not chip.
Tamper proof machine screws of this type are quoted from M1 to M14; the recorded configuration covers that range in stainless 304 with a pan head and a pin-style security recess. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission, because the thread length and the recess size both have to be set before the die is cut.
| Item | How it is defined | What we control |
|---|---|---|
| Head diameter and height | The pan head that bears on the panel | Checked on the projector on the first article |
| Recess type and size | Which security bit is required | Checked with the matching bit |
| Pin position and height | Where the pin sits in the recess | Checked on the first article |
| Thread size and pitch | The fit in the tapped hole | Gauged per batch |
| Length | From under the head to the tip | Measured on the shop plate |
| Passivation | The condition of the stainless surface | Checked on the sample |
Each size is quoted against the panel it closes. The head diameter, the counterbore or clearance in the panel and the thread engagement are reviewed together, because a security head that is right for one housing stands proud in another even at the same nominal size.
Length is measured from under the head, and the recess is checked with the bit that will be used to service the joint. That last point matters more than it looks: if the customer’s service team does not have the matching bit, the panel will be opened with a drill, and the security feature will have failed at the design stage.
The security recess is the whole point of the part, and it is the feature that has to be chosen against the threat rather than against a catalogue. Each drive has a characteristic failure mode, and each needs a specific tool to open it without damage.
| Drive | How it resists | What it needs to open | Best for |
|---|---|---|---|
| Pin in the recess | A standard bit cannot seat because the pin blocks the centre | The matching hollow-bit | Panels opened rarely, by a known service team |
| One-way slot | Only turns one way, so it cannot be unscrewed | Cut slot or drill | Permanent fixings, no service access needed |
| Four-lobe with pin | No standard driver fits the lobes and the pin together | The matching security bit | Access panels on equipment in public areas |
| Spanner (two-hole) | Two small holes instead of a slot | Pin spanner | Vending, meters and signage |
| Torx with pin | The pin blocks a standard Torx bit | Torx-Plus or hollow Torx | Electronics housings and enclosures |
None of these is unopenable. The pin can be drilled, the one-way slot can be cut, and the matching bits are sold openly. What a security screw does is raise the effort above casual interference, and leave evidence: a turned or drilled head is visible to the person who checks the equipment.
Torque is the other half of the design. A security head is usually driven with a small tool and a low torque, so the joint has to be specified for that. Over-driving a pin-style recess with a driver that is not aligned bends the pin or deforms the recess, and the screw then cannot be removed without drilling.
The head has to be matched to the panel. A pan head spreads the clamp load and covers the hole; a binding head, where the drawing calls for it, gives a slightly taller, flatter profile for a bound stack. Both are formed so the recess sits in the centre where the material is thickest.
This tamper proof machine screw is supplied passivated, with no coating. The passivation removes free iron left by forming and restores the chromium oxide film on the stainless surface, which is what keeps the screw from rusting through the service life of the panel it holds closed.
| Finish | How it protects | Effect on recess and thread | Typical use |
|---|---|---|---|
| Passivated stainless | Free iron removed, film restored | No dimensional change | Outdoor panels and equipment housings |
| Electropolished | Surface levelled, chromium enriched | A few microns removed; recess re-checked | Visible security hardware |
| Black oxide (stainless) | Chemical conversion, thin film | Minimal thickness; recess re-checked | Dark panels where a bright head draws attention |
| Zinc plated (steel equivalent) | Sacrificial layer | Build-up in the recess; bit re-checked | Steel security screws indoors |
| Ceramic or PTFE coated (steel) | Barrier layer | Thicker film; recess re-checked | Steel screws in aggressive service |
Salt-spray exposure is agreed per project and written on the drawing; passivated stainless is tested in the condition it ships in. On a security screw the finish also affects the evidence: a coating that chips shows that the head has been turned, but it also leaves a rust trap around the chip, so passivated stainless is the usual choice for exposed panels.
Packing protects the recess and the thread. The parts are bagged in counted quantities and labelled with the batch, the material heat and the drive type, because two security screws that look alike but take different bits will cause a service call that the part was meant to prevent.
Three installations where a closed panel has to stay closed unless the right person opens it:
Vending and self-service machines
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Security screws on a vending machine door |
Access-control housings and terminals
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Security screws on a self-service terminal panel |
| Where it sits | The screw closes a meter cover or a distribution box that only the utility or the building operator may open. |
| When it goes wrong | A cover that opens with a common tool allows tampering that is hard to prove, and a stripped head leaves the box unsealed. |
| Why it happens | The box is in a public or shared space, the seal is part of the record, and the fixing is inspected on a schedule. |
| What we control | Recess type checked against the operator’s tool, the pin height measured, and the thread gauged per batch. |
Four reasons that matter on a security part, each tied to what the drawing has to prove:
|
Drive chosen against the threat and the service team
The recess type, the pin height and the tool the customer will use are reviewed before the die is cut, so the joint can still be opened when it has to be. Basis: Drive, pin and service tool reviewed before tooling. |
Head and recess formed in one operation
The pan head and the security recess are formed in the heading die, so the pin is part of the head and cannot be removed on its own. Basis: One heading operation for head and recess. |
|
Recess and pin checked with the bit
The recess is driven with the matching bit and the pin position is measured on the projector, on the first article. Basis: Recess and pin checked on the first article. |
First article to repeat production
Everything that decides the batch – drawing revision, wire heat, die set, thread roll – is fixed at the first article and reused for repeats. Basis: First article signed off before the batch is released. |
Shi Shi Tong forms these tamper proof machine screws on a single-die header that upsets the pan head and forms the security recess, pin included, in one operation, then rolls the machine thread and passivates the parts. The first part of every run is measured on the head, driven with the matching bit and gauged on the thread before the batch continues.
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Between runs the die insert is changed to the drawing recess and pin, and the thread rolls to the size; the first part goes to the projector, to the bit and to the gauges before the run continues. The drive type is written on the batch record, so a repeat order is never packed with the wrong recess.
What decides whether a tamper proof machine screw passes is the head diameter and height, the recess type and depth, the pin position, the thread class and the passivation. The inspection agreement covers those, and the criteria come from the drawing.
Recess and pin on the projector |
Thread gauged per batch |
Hardness testing where the drawing requires it |
Salt-spray testing of the passivated part |
Each batch is recorded against the drawing revision: head and recess from the first article, the thread gauged per batch, and the drive type carried on the label. If the bit or the pin check fails, the parts back to the last good setting are held and re-checked.
A report from an outside laboratory, where one is required, is organised before the batch runs so it can be filed under the same batch number.
Every shipment of tamper proof machine screws is traceable to the wire it was made from. The grade, heat number and standard 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 finish. 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 security screws the first article is driven with the bit the service team will carry, so the recess and the pin are signed off with the tool, not only on the projector. Buyers visit during the process to review samples and to see how the recesses are formed.
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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 header and the inspection room 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 |
It is a machine screw whose drive cannot be turned with an ordinary screwdriver or bit. This one is stainless 304 with a pan head and a pin-style security recess, quoted from M1 to M14 with a machine thread.
No. It raises the effort above casual interference and leaves evidence on the head. Any security drive can be opened with the right bit, and most can be defeated with effort; what the part does is keep opportunity out and make tampering visible.
The one that matches how often the panel is opened and who opens it. A panel that the service team opens monthly takes a pin-style recess and a hollow bit; a permanent fixing with no service access can use a one-way slot.
With a pin-style or Torx-pin recess, yes, as long as the head has not been damaged. One-way slot screws are destroyed on removal, and a head that has been drilled is not re-usable.
Passivated stainless is the standard, with electropolishing or black oxide where a different appearance is wanted. Plated steel equivalents are available, but the coating has to be re-checked in the recess.
Head diameter and height, security recess type and size, pin position, thread size and pitch, length and datum, material and grade, finish, and the bit the service team will use.
How a tamper proof machine screw project runs from drawing to repeat delivery:
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1
Send the drawing or sample
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→ |
2
Drive and service tool review
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→ |
3
First article with the matching bit
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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, security recess type and size, pin position, thread size and pitch, length and its datum, material and grade, finish, and the bit the service team will use.
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Head diameter and height
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Security recess type
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Pin position
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Thread size and pitch
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Length and datum
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Service bit and material
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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
