Hex Socket Head Shoulder Screw

We make hex socket head shoulder screws in carbon steel with a black zinc plate, a knurled cap head and a ground shoulder, quoted to the drawing. The socket drives on the axis and the knurl allows adjustment by hand, and the socket and shoulder are re-checked after plating.

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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 Hex Socket Head Shoulder Screws Are

A hex socket head shoulder screw has an internal hexagon in the head, a knurled or plain cap head on top, a ground shoulder that locates the part, and a smaller machine thread behind it. The part recorded here is carbon steel with a black zinc plate, quoted from M1 upward with the shoulder made to the drawing.

Hex socket. An internal hexagon driven with an Allen key, sized to the head.

Cap head. A cylindrical head, often knurled on its outside so it can also be turned by hand.

Ground shoulder. A precision diameter that sets the position of the part and the depth of the thread.

They are used on equipment that has to be adjusted and then locked, and on assemblies where the head sits inside a counterbore that a wrench cannot reach. The same screw is often turned twice in its life: once by hand during setup, and once with a key when the setting is fixed.

Two Ways to Drive, One Shoulder to Seat

On a hex socket head shoulder screw the head offers two places to apply torque. The socket is the precise one: an Allen key turns the screw from inside the head, so the driving force stays on the axis and the head does not need to be reached from the side. That is what allows a cap head to sit inside a counterbore and still be tightened.

The knurl is the other. On many of these screws the outside of the head is knurled, and the knurl is not decoration: it lets the part be turned between finger and thumb during adjustment, held in a collet for machining or assembly, or turned with a soft-jaw wrench where a key would not fit. A knurled head is what makes a shoulder screw usable as a hand-adjusted locating pin as well as a fixed fastener.

The shoulder then does the work neither drive can do. It sets the depth at which the screw stops, and it carries the part that pivots or slides on it. That is why the shoulder is ground rather than turned to size: a locating diameter that is a few hundredths out will not pass through the bore at all, or will let the part move.

The socket size and the head diameter are linked. A socket that is too large leaves too little wall in the head; too small and the key cannot transmit the torque the thread needs. On a small screw this trade is tight, which is why the socket has to be specified with the head rather than chosen from a standard table.

The black zinc plate adds the fourth consideration. It is applied after grinding, so it is a film on the shoulder as well as on the head. On a locating fit that film is a dimension, and the drawing has to say whether the shoulder size applies before or after plating.

Head, Socket and Shoulder

The part is quoted to the drawing with the head, the socket and the shoulder stated separately. Custom lengths up to 2,000 mm, subject to DFM review after drawing submission. The quotation for hex socket head shoulder screws carries the head diameter and height, the socket size and depth, the shoulder diameter and length, the thread, and the plate specification.

The socket depth is the dimension that limits the key. A socket that is deep enough for the full key engagement transfers more torque, but it takes material from the head; on a low cap head there is a point where the remaining section over the shoulder is too thin.

The knurl is specified by pattern and depth when the head has one. Two knurls of the same depth but different pitch feel different in the hand, and a knurl that is rolled too deep leaves a thin wall around the socket.

The shoulder is agreed against the bore, as on any locating part. On a plated screw the pair is checked in the plated state, because that is the part the customer assembles.

What Hex Socket Head Shoulder Screws Give and Costs

Four properties decide hex socket head shoulder screws, and each one carries a cost:

The value is control. The socket gives a tighter, more repeatable torque than a cross recess, and the knurl gives a way to turn the same screw by hand during adjustment, so one part can be both adjusted and locked.

The cost is the head. A socket removes material from the centre of a head that has to stay short, and a knurl removes material from its outside; on a small screw those two decisions are made together.

Black Zinc and the Ground Shoulder

The recorded finish is black zinc plated. It gives a dark, uniform appearance with a sacrificial layer, which suits equipment where the fixing is visible and should not shine, and it costs less than a stainless part of the same strength.

Surface Options for Hex Socket Head Shoulder Screws

Where the shoulder is a locating fit, a plate on it is a film inside the fit. On a tight bore the film is enough to stop the screw entering cleanly; on a loose one it is enough to add play. That is why the drawing states the plating spec and whether the shoulder is masked.

Inside the socket, the plate matters for the key. A heavy layer reduces the effective across-flats, and a key that is a fraction too large will not enter. The socket is checked with the key after plating on a sample from each batch.

Where Hex Socket Head Shoulder Screws Are Used

Three assemblies where a locating pivot has to be adjusted and then locked:

Why Shi Shi Tong for Hex Socket Head Shoulder Screws

Four reasons that matter on a part where two drives and one fit share the same head, each tied to something the drawing or the first article proves. All four show in the sample.

How Hex Socket Head Shoulder Screws Are Made

These screws are turned from carbon steel bar, with the cap head formed, the knurl rolled where specified, the socket broached or milled, the shoulder ground and the thread cut; the parts are then black zinc plated. The first piece of every run is measured on head diameter and height, knurl, socket across flats and depth, shoulder diameter and length, and thread.

Cutting the socket is the operation that limits the head. The across-flats and the depth are both set from the key, and the remaining wall around the hexagon is what carries the torque. A socket cut a little deep leaves a thin section over the shoulder, and that section fails when the key is turned hard.

The knurl is rolled before the socket is cut, so the socket works on a head whose outside is already finished. Rolling keeps the grain continuous and leaves a ridge that does not cut the hand; a cut knurl can leave a burr at the shoulder end that the user meets.

Grinding the shoulder before plating is what makes the locating diameter, and the plate then adds to it. Where the joint is tight, the shoulder is masked during plating or the diameter is re-checked in the plated state, and the socket is always checked with the key after plating.

Inspection: Socket, Shoulder and Plate

What decides whether hex socket head shoulder screws pass is the socket, the shoulder and the plate. The inspection agreement covers those, and the criteria come from the drawing.

Socket and shoulder on the projector	Thread and start checked
Core hardness checked	Salt-spray testing of the black zinc

The socket is measured across flats and for depth, and checked with the key on a sample from each batch. A socket that measures right but will not take the key is usually a burr at one corner, and a key that rocks in the socket is usually too much depth.

The shoulder is measured for diameter, roundness and length. On a plated part the measurement is taken in the plated state, because the film is part of the delivered size.

The head is checked for diameter, height and the knurl, and the plate for coverage inside the socket and on the shoulder. The plate is also checked in the salt-spray chamber on a sample from each lot, since black zinc is a sacrificial finish whose edges go first.

Certificates and Material Documentation

Every batch of hex socket head shoulder screws is traceable to the bar 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 plating report carries the layer thickness and the lot number.

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 socket and the shoulder, and the plating report. The records carry the drawing revision and the batch number, so a repeat order of hex socket head shoulder screws seats the same way.

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 plated locating part the first article is fitted into the customer bore and driven with the customer key, because both the fit and the socket are affected by the plate. 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 machining cell 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

Technical Guides

What a Shoulder Screw Is How a stepped fastener locates a joint, and what the drawing has to state. Read the guide

Multi-Step Shoulder Screw Design When one shoulder is not enough, and what each step has to state. Read the guide

Products

Hex Socket Shoulder Screws The low head socket version in steel. Hex Socket Shoulder Screws	Hexagon Socket Shoulder Screws The hexagon socket head shoulder version. Hexagon Socket Shoulder Screws	Stainless Socket Shoulder Screws The stainless shoulder screw with a socket drive. Stainless Socket Shoulder Screws
Metric Precision Shoulder Screws The precision metric shoulder fastener series. Metric Precision Shoulder Screws	Shoulder Screws The socket head version in stainless. Shoulder Screws	Stainless Steel Shoulder Screws The stainless cap head version with a cross. Stainless Steel Shoulder Screws

Hex Socket Head Shoulder Screw FAQ

Order Hex Socket Head Shoulder Screws

How a hex socket head shoulder 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.