Metric Socket Head Cap Screw

We make metric socket head cap screws in copper with a plain finish, quoting them from M1 to M10 with lengths made to the drawing. The copper grade and the assembly torque are agreed together, and the first article is assembled and measured across the 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 Metric Socket Head Cap Screws Are

A metric socket head cap screw is a machine screw with a cylindrical head and an internal hexagon, made to the metric thread system. The part recorded here is copper with a plain finish, quoted from M1 to M10 with the small sizes in the same range.

Metric thread. A 60 degree thread defined by a nominal diameter and a pitch, with a coarse pitch that is standard for each size.

Cap head. A cylindrical head with a flat bearing face and a deep socket, the form that takes the most torque for its diameter.

Hexagon socket. An internal hexagon driven with a key, engaged on six flats rather than on four arms.

Copper body. Nearly pure copper: conductive, thermally efficient, non-magnetic, and soft enough that the socket is the first feature to deform.

They are used on busbars, test fixtures, thermal assemblies and earth bonding points, where the fixing is part of the current or heat path and the head has to be driven from inside a small space.

How a Socket Drive Becomes the Limit in Copper

A hexagon socket is the most efficient drive for a given head diameter: six flats, a key that seats to the floor, and no cam-out ramp. On steel or stainless that makes the socket stronger than the thread, so the joint is limited by the screw’s strength rather than by its drive.

Copper changes the order of failure. The metal is soft, so the corners of the hexagon yield before the thread strips, and the yield is concentrated exactly where the key bears. That means the practical torque limit on a metric socket head cap screw in copper is set by the socket, not by the diameter of the thread or the strength of the material in tension.

The head height then becomes the constraint on the constraint. A cap head has more height than a button or a countersunk head, which is why the socket can be deep; but copper’s lower stiffness means the head deflects a little more under the same clamp, and the wall around the hexagon takes more of that movement. On the small sizes the margin narrows quickly, which is why these parts are usually specified at a modest torque and used where the load is carried by the joint rather than by the screw alone.

Galling is the second behaviour to plan for. Copper seizes against itself and against many metals when the surfaces are clean and dry, and the seizure happens during assembly rather than in service. A joint that will be opened more than once needs an agreed practice: a lubricant, a different material for the mating nut, or a torque and speed that do not generate heat.

What copper gives in exchange is the reason it is used at all. It conducts better than brass, transfers heat better than any steel, and does not respond to a magnet. Where the fixing is part of the circuit or the thermal path, those properties are the specification, and the softness is the price.

Sizes, Head and Socket

The recorded range is M1 to M10, with the small sizes quoted in the same envelope and 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 metric socket head cap screw carries the diameter and pitch, the head diameter and height, the socket size and depth, the length and the copper grade.

The grade is the first line because the properties being bought depend on it. A drawing that says copper without a grade leaves the choice to the supplier, and the difference shows on a certificate rather than in the hand.

Socket depth is measured against the head height, and on copper it is worth keeping as deep as the head allows. A shallow socket in a soft metal is a socket that will mark on the first serviced joint.

Length is measured over the head. On a busbar or a terminal the usable thread length is the overall length minus the stack, and on copper that engagement is what limits the joint rather than the screw’s strength.

What a Metric Socket Head Cap Screw Gives and Costs

Four properties decide metric socket head cap screws in copper, and each one carries a cost:

The value is a fixing that is part of the electrical or thermal path rather than an insulator in the middle of it, driven with a key that fits inside a head no larger than the thread requires.

The cost is that the drive, not the thread, limits the joint. The torque has to be set for the socket and the alloy, and that means it is written on the drawing rather than judged at the bench.

Plain Copper and the Alternatives

The recorded finish is plain, so the alloy is the surface. On a part chosen for conductivity that is the right default: a coating at a conducting joint adds resistance, and on a copper thread it also changes the fit in a tapped hole.

Surface Options for Metric Socket Head Cap Screws in Copper

Tinning is the usual compromise on electrical parts: it keeps the copper from oxidising in storage while adding a layer thin enough that the joint still conducts. Where a coating is used, the socket is gauged after plating, because the copper underneath has less margin than steel would.

Plain copper darkens quickly in air and faster in a hand. That is not a defect, but it means the finish is described as a condition rather than a colour, and the customer’s sample is the reference.

Where Metric Socket Head Cap Screws in Copper Are Used

Three settings where conductivity and a compact drive matter together:

Why Shi Shi Tong for Metric Socket Head Cap Screws

Four reasons that matter on a soft-metal part driven by a socket, each tied to something the drawing or the certificate has to show:

How Metric Socket Head Cap Screws Are Made

These screws are turned from copper bar, with the cap head and the hexagon machined in the same setup and the thread cut behind it; the parts are then left plain or finished as specified. The first piece of every run is measured on head diameter and height, socket size and depth, thread, grade and length.

Machining the hexagon in the same setup as the head is what keeps the socket on the head axis. In copper the cut is easy; the difficulty is tool sharpness, because a dull tool smears the metal instead of cutting it, and a smeared wall in a hexagon is a wall that grips the key unevenly and marks early.

Threading copper needs the same attention. A cut thread is predictable and leaves a clean flank; a rough one holds swarf and galls on the first assembly. The tool condition and the cutting parameters are recorded with the job rather than adjusted at the machine.

Because the parts are left plain, handling is part of the process. Copper tarnishes where it is touched, so the screws are handled with gloves at final inspection and packed so they do not rub bright spots into each other.

Inspection: Grade, Socket and Thread

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

Socket depth and walls on the projector	Thread and start checked
Hardness against the copper grade	Humidity exposure on the plain surface

The grade is confirmed on the material certificate for every heat, because it is what the part was bought for. Head diameter, height and socket depth are measured together on the projector, and the socket is then proved with the production key.

The functional check is a drive at the torque the joint uses, followed by removal and inspection of the hexagon corners under magnification. In copper that cycle shows the start of corner yield before it becomes visible on the outside of the head.

Where the screw is part of a current path, a sample is also checked for contact resistance across the joint before and after the assembly cycle, since a face that is not flat shows as a resistance that changes.

Certificates and Material Documentation

Every batch is traceable to the copper stock it was made from. The grade and heat number appear on the material certificate supplied with the parts, and the inspection record carries the measured head and socket against 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, and the RoHS report for the grade. The documents carry the drawing revision and the batch number, so a repeat order of metric socket head cap screws matches the electrical behaviour of the original.

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 copper part the first article is assembled at the agreed torque and checked for seizure. 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 turning cell and the inspection bench 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

Hex Socket Screw Specification Table Socket size and head height against diameter, across the socket family. Read the guide

Screw Fastener Thread Types How thread form and pitch behave in soft metals. Read the guide

Products

Copper Machine Screws The pan head copper version of this family. Copper Machine Screws	Brass Socket Head Cap Screws The brass socket version for comparison. Brass Socket Head Cap Screws	Socket Head Cap Screw The standard steel cap head. Socket Head Cap Screw
Low Head Socket Head Cap Screws A reduced head in carbon steel. Low Head Socket Head Cap Screws	Anodized Aluminum Screws The aluminium equivalent for weight-led joints. Anodized Aluminum Screws	Metric Knurled Thumb Screws Tool-free drive for the same panels. Metric Knurled Thumb Screws

Metric Socket Head Cap Screw FAQ

Order Metric Socket Head Cap Screws

How a copper 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.