Flanged Socket Head Cap Screw

We make flanged socket head cap screws in black zinc plated carbon steel, a tall cap head with a deep hexagon socket and an integral flange that acts as a washer, quoting them from M1 to M14. Flange dimensions, socket, thread and joint torque are agreed up front, and the first article is tightened in your own joint.

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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 Flanged Socket Head Cap Screws Are

A flanged socket head cap screw is a socket head screw with a wide integral flange at the base of the head, so a washer is built into the part. The socket gives the torque, the flange gives the bearing area, and the machine thread clamps the joint. This family is made in carbon steel with a black zinc plate, quoted from M1 to M14 with Number 219.

Cap head. A tall cylinder with a flat top and a deep hexagon socket, made to be tightened hard.

Integral flange. A collar turned out under the head, acting as a washer that cannot be lost or forgotten.

Hexagon socket. An internal hexagon that takes a key, with enough depth to carry high torque.

Black zinc. A dark sacrificial zinc deposit over the finished screw.

In practice a flanged socket head cap screw is specified together with the torque it will carry, because under a socket head the flange is a bearing surface rather than a decorative collar.

A Flange Under a Screw You Can Torque

A flange is easy to draw and easy to get wrong, and the reason is that its job changes with the head above it. Under a low head the screw cannot be tightened far, so the flange mostly spreads a gentle load. Under a socket head cap screw the joint can be tightened to a real preload — and then the flange stops being a spacer and becomes a washer carrying that preload on a ring a few tenths thick.

That is the difference between this part and a flanged button head. The socket gives a deep, strong drive, so the assembly can reach a torque where the flange has to stay flat. A flange that is too thin dishes under that load: the outer edge digs into the panel, the centre lifts, and the preload quietly drops as the metal yields. The joint feels tight when it is made and is not tight a week later.

The seat matters for the same reason. At low preload a slightly uneven seat is absorbed; at high preload the same unevenness tilts the whole head and puts the load on one side of the flange. That is why a flanged cap screw on a cast or a welded boss wants a machined spot face rather than as-cast surface — the flange cannot conform the way a separate washer can.

The flange also removes a component, which is the everyday benefit. No washer to stock, feed or drop, no washer to be missing on the one joint that matters, and no gap in the stack to be lost when the washer is omitted. On an assembly with hundreds of fixings, that is why the form is chosen before anyone thinks about load.

The black zinc plate follows the same logic as on any dark internal assembly. It is thin enough not to close the socket, and it is sacrificial, so a scrape at the flange edge does not begin a rust line. Where the joint is exposed, the stainless version of the same geometry is the answer, and the flange behaves identically.

Sizes, Flange and Head Height

The recorded range is M1 to M14, covering M1, M2, M3, M4, M5, M6, M7, M8, M9, M10 and M14. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. For a flanged socket head cap screw the quotation carries head diameter and height, flange diameter and thickness, socket size and depth, and the thread, because the flange is the bearing surface and the socket is the drive.

Flange thickness is the number that decides whether the part works at the torque it will be used at. It should be on the drawing with the flange diameter, because two flanges of the same diameter and different thickness behave quite differently: the thin one dishes, the thick one holds. Where the joint is tightened to a specified torque, this is not a detail to leave to the maker.

Length is measured from under the flange, because the flange is the bearing face. A customer who switches from a plain socket head plus washer to a flanged version should expect the stack to change, and the same length may no longer be right in a blind hole.

Preload, Flange and One Less Part

Three features define this part: the deep socket, the integral flange and the black zinc. The first allows high preload, the second carries it over a ring, and the third protects the screw in a dark interior.

The socket is what distinguishes this part from a flanged button head, and the difference is not cosmetic. A button head is low, so its socket is shallow and the torque it can take is limited; a cap head has the height to carry a deep socket, so it can be driven to the preload the joint was designed for. Under that load the flange has to be a washer, not a decorative collar.

The one-less-part argument is the reason the form sells. Fewer components means fewer parts to keep in stock, fewer things to drop into a machine, and a stack that does not change when someone forgets the washer. On a line building hundreds of units a day, that is worth more than the small extra cost of turning out a flange.

Black Zinc Under a Loaded Flange

The recorded finish is black zinc over carbon steel. On a flange the deposit is doing work in a place nobody sees: water and oil collect in the annular recess between the flange edge and the panel, so the underside of the flange is where corrosion starts first, and where the plate has also been scraped by the seat.

Finish Options for Flanged Socket Head Cap Screws

Where the joint is indoors and the part is hidden, black zinc is enough and it is the cheapest dark finish. Where the joint is outside, the stainless version of the same screw is the right part, and the flange behaves identically — the geometry does not change, only the corrosion story.

The flange also changes how the finish wears. A plain head loses its plate at the socket, where the key works; a flanged head loses it at the flange edge, where the load is concentrated and where water sits. Both are wear points that a coat of plate cannot prevent, which is why the sacrificial option is the practical one on steel.

Where Flanged Socket Head Cap Screws Are Used

Three assemblies where flanged socket head cap screws are the fixing:

Why Shi Shi Tong for Flanged Socket Head Cap Screws

Four reasons that matter on a part that carries preload through a flange, each tied to what the drawing has to prove:

How These Screws Are Manufactured

Shi Shi Tong forms these flanged socket head cap screws from carbon steel wire on single-die headers that form the cap head, the flange and the hexagon in one stroke, rolls the machine thread to a blunt chamfered end and plates the parts in black zinc. The first part of every run is measured on the head and flange, driven with the production key and entered into a thread gauge before the batch continues.

The flange is formed in the same stroke as the head, from the same wire, so it is as hard as the rest of the screw — which is what lets it act as a washer under load. A flange that has been softened, or one that is too thin, will dish before the joint reaches its torque, and the failure is invisible because it happens on the underside where the flange meets the panel.

Inspection: Flange, Socket and Thread

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

Flange and head on the projector	Thread gauged per batch
Hardness checked on the wire	Salt-spray testing of the plate

The flange is checked for diameter, thickness and face flatness on the projector, and the transition from the flange into the head is inspected at magnification, because that is where a flanged screw cracks under torque. The socket is checked across flats and for depth and then driven with the production key.

The thread is gauged per batch and the plate is checked for thickness and adhesion with attention to the flange underside. The first article is tightened to the joint torque on a test plate and then checked for flatness again, because a flange that survives measurement and not load is the failure this part is prone to.

Certificates and Material Documentation

Every shipment of flanged socket head cap 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 plating record is kept with the inspection file.

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 plating. The documents carry the drawing revision and the batch number, so a repeat order is made to the same flange geometry that was approved.

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 a flanged screw the first article is fitted and tightened in the customer’s joint, because the flange carries the load. Buyers visit during the process to review samples and to see how the heads and flanges are formed.

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

Related Products and Guides

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Flanged Socket Head Cap Screw FAQ

Order Flanged Socket Head Cap Screws

How a flanged socket head cap 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.