Security Socket Head Cap Screw

We make security socket head cap screws with a pin-in-hex drive, in carbon steel with an eco black zinc finish, quoting them from M1 to M10. Pin height, pin diameter and socket depth are agreed as one relation, and the first article is driven with your own hollow 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.

What Security Socket Head Cap Screws Are

A security socket head cap screw is a socket head cap screw with a tamper-resistant drive: in the form recorded here, a hexagonal socket with a pin standing in its centre. The part is carbon steel with an eco black zinc finish, quoted from M1 to M10 with lengths made to the drawing.

Cap head. A cylindrical head with a flat bearing face, taller than a button head, carrying a deep socket.

Pin-in-hex socket. A hexagon with a central pin, so an ordinary Allen key cannot seat.

Machine thread. A uniform thread for a tapped hole or a nut, with the length measured over the head.

Eco black zinc. A trivalent zinc with a dark passivate, free of hexavalent chromium, low in reflection.

They are used on access covers, control boxes, meter enclosures, display fixings and equipment that the owner does not want opened by anyone who happens to have a standard key: street furniture, public facilities, kiosks, vending and building services.

The Security Is in the Drive, Not the Head

People describe these parts by their head, but nothing about the head is secure. A cap head can be gripped, a button head can be gripped, and the thread is the same thread as any other screw. What makes a security socket head cap screw different is a single feature inside the socket: a pin in the middle, which stops an ordinary hex key from reaching the flats.

The pin does no work. All of the torque is carried by the six flats around it, and the pin simply occupies the space a standard tool would need. That has a practical consequence for the joint: the driver is a hollow-tipped key, and the engagement area is reduced by the volume of the pin, so the socket has to be deeper and better cut than on an ordinary cap screw of the same size.

That leads to the tolerance that matters most, which is the height of the pin. If the pin stands too proud of the socket floor, a hollow key bottoms out on the pin before the flats engage and the drive slips; if the pin is set too low, an ordinary key can be ground or entered at an angle and the part is no longer a deterrent. The pin height, pin diameter and socket depth are one relationship and are specified together.

The honest framing is that this is a deterrent, not a lock. A determined person with the right tool, or with a slotted driver that clears the pin, will remove the screw. What the pin buys is that the ordinary key in a maintenance bag does not fit, and that casual access to a panel becomes a deliberate act with a special tool.

For that reason the screw is usually paired with a head type that also resists gripping. A cap head with a smooth rim is harder to clamp than a button head, and a countersunk version of the same drive leaves nothing to grip at all. Where the cover must not be opened, the choice of head matters as much as the choice of socket.

Sizes, Socket and Pin

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 a security socket head cap screw carries the head diameter and height, the socket size and depth, the pin diameter and height, the thread and the overall length.

Pin diameter is usually a fraction of the socket across flats, and it is chosen so that a standard key of the right size cannot pass either side of it. The pairing of pin diameter and socket size is what defines which keys are excluded, so both are stated on the drawing rather than left to the supplier.

Pin height is measured from the socket floor, not from the head face. That distinction matters at inspection, because the value a driver feels is the clearance between the pin top and the flats, and it is the clearance that decides whether the hollow key seats.

Socket depth is deeper than on an ordinary cap screw of the same diameter, because the hollow key needs room for both the pin and the engagement. On the small sizes the difference is significant, and a security socket head cap screw made to an ordinary socket depth is a part that will not drive.

What a Pin-in-Hex Drive Gives and Costs

Four properties decide a security socket head cap screw, and each one carries a cost:

The value is that casual access stops being casual. A panel fixed with these screws is not opened by the first person who finds an Allen key in a drawer, and every opening becomes a decision that needs a special tool kept somewhere deliberate.

The cost is that the drive is fussier. The engagement is smaller, the key is unusual, and a technician without the right tool will damage the socket trying to use the wrong one. That is a maintenance planning problem, and it belongs in the specification rather than in the workshop.

Eco Black Zinc and What It Signals

The recorded finish is eco black zinc, a trivalent zinc with a dark passivate. It protects by sacrificial action and it looks like what it is: a fixing that is not meant to be admired. On a security fastener that is part of the function, because a bright head attracts the attention a recessed one does not.

Finish Options for Security Socket Head Cap Screws

Because the socket is deep and narrow, plating reaches the inside less readily than on an open head. A black zinc finish inside a deep socket is the first place a thin coating shows as a patch, so the socket is inspected after plating rather than only on the outside of the head.

Where the enclosure is outdoors, the honest answer is zinc nickel or stainless rather than a thicker black passivate. A public enclosure that rusts at its fixings advertises the fact that it can be opened.

Where Security Socket Head Cap Screws Are Used

Three settings where a panel must not open on the first available key:

Why Shi Shi Tong for Security Socket Head Cap Screws

Four reasons that matter on a drive whose engagement is smaller than normal, each tied to something the drawing or the tooling has to prove:

How Security Socket Head Cap Screws Are Made

These screws are headed on single-die machines that form the cap head in one stroke, broached with a hexagonal punch, pressed with the centre pin, thread rolled and zinc plated as a batch. The first part of every run is measured on head diameter and height, socket size and depth, pin diameter and height, thread and length, and driven with the customer hollow key.

Setting the pin is the operation that decides whether the part works. The pin is formed from the material inside the socket rather than inserted, so the socket is broached deeper than usual and the centre is then pressed back up to the required height. The height is set from the socket floor, and the tool that sets it is checked against a master at the start of every run.

Because the socket is deeper, the walls around it are thinner than on a standard cap screw, and the head height has to stay above the minimum for the size. A head that is pressed a little low leaves thin walls and a shallow floor, and the part still passes a socket size check while it fails as soon as a key is used.

Plating finishes the part and needs care inside the socket. A deep narrow socket traps air, and a plating line that does not allow for it leaves the inner walls patchy. The batch is inspected inside the socket, and the recess is re-proved with the hollow key after plating before packing.

Inspection: Pin, Socket and Thread

What decides whether security socket head cap screws pass is the socket, the pin, the thread and the plating. The inspection agreement covers those, and the criteria come from the drawing.

Pin height and socket on the projector	Thread and start checked
Core hardness checked	Salt-spray testing of the plated head

Pin height is measured from the socket floor on the projector, together with socket depth and across-flats. The three are read as one set, because a correct pin height in an over-deep socket is still a part that a standard key cannot drive safely.

The decisive check is functional: a standard key of the same nominal size must not seat, and the matching hollow key must seat fully and drive without the pin touching the driver. Both are tried on a sample from every lot, and the results are recorded with the batch.

A sample from every batch is driven into the customer part at the line torque and removed. That cycle shows a pin that interferes, a socket that is too shallow for engagement, or walls that begin to spread at the corners.

Certificates and Material Documentation

Every batch is traceable to the wire it was made from and to the plating lot that finished it. 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 pin height and socket depth, and the plating report. The documents carry the drawing revision and the batch number, so a repeat order keeps the same pin and the same key.

Customers and Projects

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 drives the first article is driven with the customer’s own key, because engagement depends on the tool as much as on the part. Buyers visit during the process to review samples.

Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the headers and the broaching station 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

Related Products and Guides

Technical Guides

Security Screws: What Each Drive Actually Stops How pin-in-hex, Torx pin and one-way drives differ in what they exclude. Read the guide

Tamper Proof Torx Screws The star drive with a pin, and where it suits better than a hexagon. Read the guide

Products

Pan Head Security Screws A Y drive on a pan head for smaller access points. Pan Head Security Screws	Pan Head Torx Pin Anti Theft Screw The star pin drive version. Pan Head Torx Pin Anti Theft Screw	Socket Head Cap Screw The standard socket head without a pin. Socket Head Cap Screw
Hex Socket Button Head Screw The button head with a captive washer. Hex Socket Button Head Screw	Low Profile Socket Head Screws A low head socket screw in 304. Low Profile Socket Head Screws	Cap Screw Socket Head Screw The machine-thread socket head family. Cap Screw Socket Head Screw

Security Socket Head Cap Screw FAQ

Order Security Socket Head Cap Screws

How a security socket screw project runs from drawing to repeat delivery:

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.