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+86 13143444311
Email：sst@szsst88.com
Fax：+0086-755-27322278
Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Type:M4 Shoulder Screw
Materials:Stainless Steel
Surface treatment:Plain
Head Type:Hexagon head with shoulder
Drive:External hex (wrench or socket)
Thread:Machine thread, partial
Point:Plain, chamfered
Forming:CNC turning and grinding
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10
We make M4 shoulder screws in stainless steel with a long ground shoulder and a hexagon head, with lengths made to the drawing. The shoulder length and its fit are agreed against your bore, and the first article is assembled into your mechanism and cycled.
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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.
An M4 shoulder screw is a fastening with an M4 thread, a ground shoulder that locates the part and a head that holds the assembly. The part recorded here has a long shoulder and a hexagon head, in stainless steel with a plain finish.
M4 thread. A metric machine thread that engages a nut or an insert; on this part it is smaller than the shoulder and only at the end.
Long shoulder. A ground diameter that runs most of the part’s length, so the shoulder is a shaft rather than a short locating step.
Hexagon head. An external hexagon driven with a socket or a wrench, with a flat bearing face under it.
Stainless, plain. No coating on the shoulder, so the bearing surface stays as ground.
They are used as hinge pins, linkage pivots and shaft locators in compact mechanisms, where a long bearing length is needed and the fixing has to be assembled from one side.
On M4 shoulder screws the shoulder can be a locating step, or with a long shoulder it becomes a shaft: it centres the part in the bore and the head clamps. When the shoulder is long, it stops being a step and becomes a shaft. It supports the part over most of its length, resists bending, and defines the axis the part rotates or slides on.
That changes what the drawing for M4 shoulder screws has to control. A long shoulder needs a diameter and a tolerance that suit the bore along its whole length, not just at the entry, and a bore that is tight at one end and loose at the other will bind even though both measurements are in tolerance. The shoulder also has to be square to the head, because over a long span any tilt at the head turns into a runout at the far end.
On M4 shoulder screws with a long shoulder the thread becomes secondary. On M4 shoulder screws with a long shoulder the thread only holds the assembly together: the load runs through the shoulder, and the thread sees a fraction of it. That is why the thread is deliberately smaller than the shoulder, and why the step between them is where the assembly stops rather than where it clamps.
The hexagon head contributes the drive. A wrench on the outside of the head applies the modest torque the thread needs without relying on a recess in a small head, and the flat bearing face gives the clamp somewhere to land. On a joint whose load path is the shoulder, that is exactly enough.
Stainless is chosen for the bearing surface. A long shoulder is a long bearing, and a coating on it would be a film between two sliding surfaces for its whole length; a plain stainless part keeps the ground diameter as made.
The recorded part is quoted to the drawing, with the shoulder diameter and its length stated separately from the thread. Custom lengths up to 2,000 mm, subject to DFM review after drawing submission. The quotation for M4 shoulder screws carries the shoulder diameter and tolerance, the shoulder length, the head across flats and height, the thread and the overall length.
| Item | How it is defined | What we control |
|---|---|---|
| Shoulder diameter | Ground diameter through the bore | Diameter, roundness and finish |
| Shoulder length | From the head underside | Length and squareness |
| Head | Hexagon head | Across flats, height and bearing face |
| Thread | Machine thread at the end | Size, length and start |
| Step | Transition from shoulder to thread | Position and lead-in |
| Overall length | Head face to thread end | Length and datum |
Shoulder length is the defining dimension on this part. It decides how much of the bearing surface the part has, and it must match the bore it runs in: a shoulder shorter than the bore leaves the part rocking on the head, and one that is longer than the space available prevents the assembly closing.
The shoulder diameter is agreed against the bore, and on a long shoulder the tolerance has to hold over the whole length rather than at the entry. That is a machining requirement as much as a drawing one, and it is checked on the first article at both ends.
The thread length at the end is short by design. It only has to hold the assembly, and a long thread would put thread inside the bearing bore, which is the one thing a shoulder part must avoid.
Four properties decide M4 shoulder screws with a long shoulder, and each one carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Long shoulder | A bearing surface over most of the length | Bore must be in line along its whole length |
| M4 thread | Holds the assembly together | Only a fraction of the joint’s load |
| Hexagon head | Drive from outside the head | Needs clearance for a socket |
| Stainless body | Shoulder keeps its finish | Galls in a dry stainless bore |
The value of M4 shoulder screws with a long shoulder is a single part that replaces a pin and a fastener. Where a linkage needs a long bearing and has to be assembled from one side, the long shoulder screw is both the pivot and the fixing.
The cost is precision over a length. A long shoulder is only as good as the bore it runs in, and any misalignment between the bores along the assembly becomes a binding pivot rather than a loose one.
The recorded finish is plain. On a long shoulder that is not a cosmetic choice: the shoulder is a bearing surface over most of its length, and a coating on it would be a film that wears along the whole sliding contact rather than at a point.
| Option | How it protects | Effect on the long shoulder | Typical use |
|---|---|---|---|
| Passivated, plain | Removes free iron; rebuilds oxide | No build; shoulder as ground | Default for stainless |
| Electropolished | Levels the surface | Bearing finish improved | Clean and food equipment |
| Black oxide on stainless | Colours the surface | Thin film; fit unchanged | Dark mechanisms |
| Nickel plated | Hard bright barrier | Build over the whole length | Where a bright finish is wanted |
| Hard chrome steel | Hard wear surface | Build; shoulder re-ground | High-cycle steel pivots |
Where a coating is applied, the shoulder is ground after plating so the fit is restored. On a short shoulder that is a small operation; on a long one it is most of the part, which is why a plain stainless shoulder is usually the simpler route.
Electropolishing is the finish that improves a long bearing surface without changing its dimensions measurably, which is why it appears on pivots in clean equipment.
Three settings where a long bearing is needed and access is from one side:
| Where it sits | The screw runs through the knuckles of a hinge and holds the assembly together from one side. |
| When it goes wrong | A shoulder shorter than the knuckle stack lets the hinge rock, or a bore that is out of line binds it. |
| Why it happens | The bearing is long, the assembly is small, and the joint is serviced. |
| What we control | Shoulder length and bore alignment checked; first article assembled and cycled. |
| Where it sits | The screw locates a lever over a long span where the movement must be smooth. |
| When it goes wrong | A shoulder with a taper binds at one end and the lever sticks. |
| Why it happens | The movement is precise, the span is long, and the joint is adjusted. |
| What we control | Diameter measured at both ends; first article checked for free movement. |
| Where it sits | The screw locates a small roller or a bushing where the shoulder acts as its axle. |
| When it goes wrong | The shoulder is undersize and the roller rattles, or it is oversize and will not enter. |
| Why it happens | The part rotates, the bore is a bearing, and the fixing is small. |
| What we control | Fit agreed with the bore; first article assembled and rotated. |
Four reasons that matter on a part whose shoulder is a long bearing, each tied to something the drawing or the first article has to prove:
|
Shoulder length and bore stated
The shoulder length is agreed against the bore it runs in, because a long shoulder shorter than the bore leaves the part rocking on the head. Basis: Length and bore agreed. |
Turned and ground along the length
The shoulder is machined and ground along its whole length, so the diameter holds at the far end as well as at the entry. Basis: Ground along the length. |
|
Diameter measured at both ends
The shoulder is measured at several points along its length and for roundness, because a taper is the failure mode on a long bearing. Basis: Measured at both ends. |
Same fit across orders
The grinding setting is recorded with the drawing revision, so a repeat order runs the same bore the same way. Basis: Same fit across orders. |
These screws are turned from stainless bar, with the long shoulder, the hexagon head and the thread machined in one setup and the shoulder ground along its length; the parts are then passivated. The first piece of every run is measured on shoulder diameter at several points, roundness, shoulder length, head across flats and the thread.
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Grinding a long shoulder is where M4 shoulder screws are decided. The diameter has to hold at the far end as well as at the entry, and a wheel that wears across the length leaves a taper that no single measurement reveals. That is why the shoulder is checked at several points rather than at one, and why the grinding setup is recorded with the job.
Machining the head and shoulder in one setup keeps them on one axis, which on a long part matters more than on a short one: a tilt at the head becomes a runout at the far end of the shoulder, and the part then binds in a bore that is perfectly good.
Passivation follows and reaches the whole shoulder. The bearing surface is the part of the piece that will be inside a bore, so the batch is checked there rather than only on the head.
What decides whether M4 shoulder screws pass is the shoulder diameter along its length, its roundness, its length and the head. The inspection agreement covers those, and the criteria come from the drawing.
Shoulder at both ends on the projector |
Thread and start checked |
Hardness against the stainless grade |
Salt-spray testing of the shoulder |
The shoulder is measured for diameter at both ends and at the middle, and for roundness at each point. On a long bearing that spread of readings is what shows a taper, and a taper is the difference between a pivot that turns freely and one that sticks at the far end.
The shoulder length is measured from the head underside and the head across flats with it, since the fit and the drive are the two things the customer meets. The part is then fitted into a gauge bore of the customer’s size and turned by hand.
A sample from every batch is assembled into the customer mechanism and cycled. That cycle shows the fit along the whole bearing, which no single measurement replaces.
Every batch is traceable to the heat of stainless 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 shoulder values at each point 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 with measured values, and the passivation records for the batch. The documents carry the drawing revision and the batch number, so a repeat order of M4 shoulder screws runs the same bore the same way.
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 long shoulder the first article is assembled into the customer mechanism and cycled. Buyers visit during the process to review samples.
|
8,678+
customers served
|
87%
of orders from repeat customers
|
56%
of orders through referrals
|
89
countries and regions shipped to
|
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 grinding setup 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 |
It acts as a shaft: it supports the part along its length and resists bending. A short shoulder only centres the part.
So the load runs through the shoulder and the thread only holds the assembly together. The step is where the assembly stops.
Usually a taper in the shoulder, or bores that are out of line. On a long bearing both show as stiffness at the far end.
Diameter and roundness at several points along its length, because a single measurement hides a taper.
The bearing surface stays as ground, with no coating to wear. A dry stainless bore can still gall.
Shoulder diameter and tolerance, shoulder length, head across flats and height, thread size and length, and the overall length.
How a long shoulder screw project runs from drawing to repeat delivery:
|
1
Send the drawing and the bore
|
→ |
2
Shoulder length and fit agreed
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→ |
3
First article assembled and cycled
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→ |
4
Batch production and repeat orders
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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.
For a quotation, send the drawing with the shoulder diameter and tolerance, shoulder length, head across flats and height, thread size and length, and the overall length.
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Shoulder diameter
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Shoulder length
|
Across flats
|
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Thread size
|
Thread length
|
Overall length
|
Sending a drawing? The form below does not take attachments. Email the PDF, DXF or STEP file to sst@szsst88.com with the part name and quantity in the subject line – the drawing is reviewed and a quotation follows.
+86 13143444311
sst@szsst88.com
