Low Head Shoulder Screw, Screw Manufacturer

We make low head shoulder screws in carbon steel with a colour zinc plate, a Phillips recess and a ground shoulder, quoted to the drawing. The head height is a clearance dimension, so it is controlled with its tolerance and the first article is run past the moving part.

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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 Low Head Shoulder Screws Are

A low head shoulder screw has a head reduced in height, a ground shoulder below it and a smaller thread behind the shoulder. The part recorded here is carbon steel with a colour zinc plate and a Phillips recess, quoted from M1 upward with the shoulder made to the drawing.

Low head. A head short enough that the part around it can pass over the top.

Ground shoulder. A precision diameter that locates the moving part and sets how deep the screw sits.

Smaller thread. A thread that holds the assembly together behind the step.

They are used as guide pins, stops and locating pivots, where something slides over the fixing rather than sitting on it. The same part can be a hard stop for a carriage and a locating pin for a bracket at the same time, which is why the head profile and the shoulder are specified together rather than as separate features.

Why the Head Is Low: Clearance Over the Top

A low head shoulder screw is chosen for what happens above the head. On a sliding assembly the part in motion often has to travel over the fixing, and the height of the head is what decides whether it clears. Reducing the head height is therefore not a styling decision: it is the clearance between two components that move relative to each other.

That changes what the head is for. On a conventional shoulder screw the head both drives and stops the assembly; here the shoulder usually stops it, and the head mainly carries the drive and presents a low, smooth surface. The bearing load is taken by the shoulder and by the part seat, not by the head face.

The edge of the head becomes a functional feature. A sharp edge on a low head will catch a sliding part, wear a groove in it, or produce a noise in a mechanism. A small radius on the head edge is part of the drawing, and so is the head height tolerance, because a batch that is a few hundredths high can lift the clearance to zero.

The cost sits in the recess. A low head has little material above the shoulder, and a cross recess needs depth; cutting the recess takes the section that the head would otherwise have. On the smallest sizes the recess depth is set by the head height, and the torque the screw can take is set by the recess. That is the trade that defines a low head shoulder screw.

The plate adds the last consideration. Colour zinc is chosen for appearance, and it is applied after the shoulder is ground, so it is a film inside the locating fit. Where the shoulder runs in a bore, the plate is a dimension and the drawing has to say which size applies.

Head Height, Shoulder and Thread

The part is quoted to the drawing with the head, the shoulder and the thread stated separately, and with the clearance it has to leave. Custom lengths up to 2,000 mm, subject to DFM review after drawing submission. The quotation for low head shoulder screws carries the head diameter, height and edge radius, the shoulder diameter and length, the thread, and the plate.

The head height is stated with its tolerance, because that tolerance is the clearance. A head that is at the top of its range and a sliding part that is at the bottom of its range is exactly the situation the drawing is meant to prevent.

The edge radius is a drawing feature rather than a finishing detail. On a part that rides over the head, the radius is the surface it meets, and a sharp edge will mark it.

The shoulder is agreed against the bore, as on any locating part. The shoulder length also sets how far above the panel the head sits, which feeds back into the clearance.

What Low Head Shoulder Screws Give and Costs

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

The value is a fixing that disappears into the motion of the assembly. Nothing projects, nothing catches, and the locating function is carried by the shoulder rather than by the head, so the head can be as low as the drive allows.

The cost is the drive. Every millimetre taken off the head takes a fraction of the recess with it, so a low head screw is driven at a lower torque than a standard head of the same size, and the joint has to be designed for that.

Colour Zinc and the Locating Shoulder

The recorded finish is colour zinc, a sacrificial plate with a tinted passivation. It gives a uniform appearance across a batch, which matters on equipment where the fixing is seen, and it costs less than a stainless part of the same strength.

Surface Options for Low Head Shoulder Screws

The head is the visible side, so the plate is judged there: coverage on the flat top, on the edge radius and inside the recess. A part that is low and visible shows a thin edge more than a large head would.

The shoulder is the functional side. If the plate is thick enough to change the fit, the shoulder is either masked during plating or re-checked afterwards, and the drawing states which size applies to the delivered part.

Where Low Head Shoulder Screws Are Used

Three assemblies where something moves over the fixing:

Why Shi Shi Tong for Low Head Shoulder Screws

Four reasons that matter on a fixing that has to stay out of the way, each tied to something the drawing or the first article proves. All four show in the sample.

How Low Head Shoulder Screws Are Made

These screws are turned from carbon steel bar, with the head turned low and the edge radius formed, the recess cut, the shoulder ground and the thread cut; the parts are then colour zinc plated. The first piece of every run is measured on head diameter and height, edge radius, recess depth, shoulder diameter and length, and thread.

The head height and the recess are made as a pair. The head is faced to its low height first, then the recess is cut into what is left; if the order is reversed, the recess depth can take the material the head needs and the part becomes too weak to drive. On a low head that margin is a few hundredths of a millimetre.

The edge radius is cut with the head rather than broken afterwards. On a part that is ridden over, the radius is the running surface, and a chamfer or a sharp edge will wear or catch differently from what the drawing specifies.

Grinding the shoulder before plating keeps the locating diameter on a part that is not disturbed afterwards, and the plate then adds to it. The shoulder is measured again in the plated state where the joint is tight.

Inspection: Head Height, Edge and Shoulder

What decides whether low head shoulder screws pass is the head height, the edge radius and the shoulder. The inspection agreement covers those, and the criteria come from the drawing.

Head profile on the projector	Thread and start checked
Core hardness checked	Salt-spray testing of the colour zinc

The head is measured for diameter, height and the edge radius on the projector. On a low head the height is a clearance dimension, so it is measured at several points around the head rather than at one, because a face that is tapered still measures right in the middle.

The recess is checked for depth and with the matching bit. On a low head there is a point where more depth is not better: it removes the section that the head needs, and the head then fails under the bit.

The shoulder is measured for diameter, roundness and length in the plated state. A sample is assembled with the moving part to confirm the clearance over the head, which is the property the part was chosen for.

Certificates and Material Documentation

Every batch of low 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 head height and the shoulder, and the plating report. The records carry the drawing revision and the batch number, so a repeat order of low head shoulder screws keeps the same clearance.

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 low head part the first article is fitted and the moving part is run past it, because clearance only shows in the assembly. 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 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

Choosing Washer Head Screws When a wider bearing face is worth the height it adds. Read the guide

Thread Gauge Failure After Plating Why a thread that gauged before plating can fail afterwards. Read the guide

Products

Micro Shoulder Screws A micro shoulder screw with an ultra low head. Micro Shoulder Screws	Miniature Shoulder Screws The smallest self tapping shoulder version. Miniature Shoulder Screws	Socket Head Shoulder Cap Screws The knurled socket head cap screw version. Socket Head Shoulder Cap Screws
Precision Shoulder Screws The precision version with a ground shoulder. Precision Shoulder Screws	Truss Head Shoulder Screws The truss head version in stainless steel. Truss Head Shoulder Screws	Button Head Shoulder Screws The button head version in stainless. Button Head Shoulder Screws

Low Head Shoulder Screw FAQ

Order Low Head Shoulder Screws

How a low 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.