Tel：
+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:Metric Precision Shoulder Screws Fasteners
Materials:Steel
Surface treatment:WhiteZinc Plated
Head Type:Truss Head
Drive:Per drawing; no recess
Thread:Machine thread, small
Point:Blunt
Forming:Headed
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:399
We make metric precision shoulder screws in white zinc plated carbon steel with a large shoulder, a small thread and a wide truss head, quoting them from M1 to M14. Shoulder tolerance, thread size, step face and head come from your drawing, and the first article is fitted in your bore.
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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.
These metric precision shoulder screws are fasteners whose shoulder is much larger than their thread: a wide plain section that runs in a bore, a small thread at the end, and a truss head on top. They are made in carbon steel with a white zinc finish, quoted from M1 to M14 with Number 399.
Large shoulder. A plain section sized for the bore it runs in, carrying the radial load of the joint.
Small thread. A machine thread one or more sizes below the shoulder, sized to pull the joint together rather than to bear.
Truss head. A wide, low head that spreads the clamp on a thin panel or a soft part.
White zinc. A bright sacrificial deposit over carbon steel, gauged after plating.
Metric precision shoulder screws of this kind are used where a large bearing shoulder has to be anchored in a small hole: thin-walled housings, small linkages and pivots where the thread is a retainer rather than the load path.
These parts are defined by a step. The shoulder is large and the thread is small, so at the end of the shoulder there is a shoulder face — a ring that the thread emerges from. That face is what pulls the joint: as the small thread tightens into its tapped hole, the large shoulder is drawn against the part, and the load transfers across the step rather than through the thread.
On metric precision shoulder screws that arrangement is what makes a small thread usable on a large shoulder. A thread sized for the shoulder would need a big tapped hole in the far part, and often there is no room for one; a small thread needs a small hole, and the shoulder can be as large as the bore requires. The price is that the thread carries less, which is why the joint has to be one where the shoulder does the locating and the thread only holds.
On metric precision shoulder screws the step also decides the assembly. The shoulder passes through the front part as a sliding fit and the small thread enters the far part, so the two fits have to be right at the same time: a shoulder that binds stops the thread from engaging, and a thread that is tight pulls the shoulder off line. On precision parts the shoulder diameter is toleranced and the thread is gauged, and both are measured from the same datum.
On metric precision shoulder screws the truss head is the front of the assembly. It is wide and low, so the clamp is spread on a thin panel rather than concentrated on a ring, and it has no recess — the drive is per drawing, and where a tool is needed the drawing specifies it. On a step screw the head is often the only visible surface, and a wide head is what keeps a coated panel from being marked.
White zinc is the finish across the whole part, and on metric precision shoulder screws it matters at the step face. That face is a bearing surface that is machined or formed and then plated, so the coating adds its few microns exactly where the joint seats; the parts are gauged after plating so that the shoulder and the thread are both what the drawing says.
The recorded range is M1 to M14, with shoulder diameters and lengths made to the drawing. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. For metric precision shoulder screws the quotation carries shoulder diameter and tolerance, shoulder length, thread size and length, head diameter and height, and the finish.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Truss head, wide and low | Head diameter, height and face flatness |
| Shoulder | Large plain section | Diameter, tolerance and finish |
| Step face | Ring between shoulder and thread | Squareness to the axis and finish |
| Thread | Small machine thread | Size, length and gauging |
| Material | Carbon steel | Grade and heat number on the certificate |
| Finish | White zinc plated | Thickness and gauging after plating |
| No recess | Drive per drawing | Where specified, recess depth |
On metric precision shoulder screws the ratio between shoulder and thread is the design decision, and it belongs on the drawing as two sizes rather than one. A shoulder of one diameter with a thread two sizes down is a different part from the same shoulder with a thread one size down, and the joint behaves differently because the thread load changes.
Step face squareness matters more than it looks. If the face is not square to the axis, the shoulder is pulled over as the thread tightens and the part binds in its bore; on a precision part that is the difference between a pivot and a seized one.
Three features define the part: the large shoulder, the small thread and the truss head. The first locates and bears, the second pulls, and the third spreads the clamp.
| Feature | What it gives | What it costs |
|---|---|---|
| Large shoulder | A bearing fit in a real bore | Diameter must be held through finishing |
| Small thread | Fits a small tapped hole | Carries less; holds only |
| Step face | Transfers the clamp from thread to shoulder | Must be square to the axis |
| Truss head | Clamp spread on thin panels | Needs clearance around the hole |
| White zinc | Thin sacrificial protection | Build at the step and thread |
The small thread is the practical advantage. It lets a large shoulder be anchored in a small hole, which is what a thin wall or a small boss allows, and it keeps the tapped hole out of the way of the bore the shoulder runs in.
The cost is carried by the step. All the clamp force passes through a narrow ring at the end of the shoulder, and that ring has to be square and clean; a burr there tips the shoulder in its bore and a radius there holds the joint off.
The recorded finish is white zinc plating over carbon steel. It is bright, thin and sacrificial, and on a step screw its thickness matters at three places: the shoulder diameter, the step face and the thread. All three are gauged after plating, because the coating changes each by the same few microns.
| Option | How it protects | Effect on shoulder and step | Typical use |
|---|---|---|---|
| White zinc plated | Sacrificial zinc, bright | Thin build; shoulder and thread re-gauged | Indoor general machinery |
| Black zinc plated | Sacrificial zinc, dark | Thin build; wear visible | Dark housings |
| Black oxide | Conversion film, oiled | No measurable build | Internal mechanisms |
| Nickel plated | Hard barrier deposit | Noticeable build; shoulder sized for it | Visible consumer parts |
| Stainless alternative | Passive film, no build | Shoulder and thread as made | Wet and food service |
Where a metric precision shoulder screw works wet, the material should change rather than the coating. The part is a bearing, and a plated bearing wears through at the shoulder first, in the place nobody can see.
Where the joint is dry and the part is visible, nickel is the upgrade, but the shoulder has to be sized for the deposit. On a precision part the drawing has to say which of the three routes applies: masked, undersized or ground after plating.
Three assemblies where these shoulder screws are the fixing:
| Where it sits | The shoulder runs in a bore in a thin wall and the small thread holds in a boss behind it, where a thread the size of the shoulder would have nothing to grip. |
| When it goes wrong | A shoulder that binds stops the thread engaging, and the joint cannot close. |
| Why it happens | The wall is thin, the far part is small, and the two fits are close. |
| What we control | Shoulder tolerance and thread checked; first article fitted in the bore. |
| Where it sits | The shoulder forms the pivot of a link and the small thread anchors it in a plate, so the link swings on the shoulder. |
| When it goes wrong | A step face that is not square pulls the shoulder over and the link seizes. |
| Why it happens | The joint rotates, the plate is small, and the thread is only a retainer. |
| What we control | Step face squareness checked; first article moved through its travel. |
| Where it sits | The wide truss head spreads the clamp on a thin cover and the shoulder sets the pivot line. |
| When it goes wrong | The head marks the cover, or an over-long shoulder holds the cover off. |
| Why it happens | The cover is thin, the head is visible, and the stand-off is set. |
| What we control | Head diameter and shoulder length checked; first article fitted. |
Four reasons that matter on a stepped part, each tied to what the drawing has to prove:
|
Shoulder and thread agreed as a pair
Shoulder diameter and tolerance, thread size, step face and head are agreed as one set, because on these metric precision shoulder screws the step is the joint. Basis: Shoulder and thread agreed as a pair. |
Turned or headed, then gauged at the step
The head and shoulder are formed with the step face square, the thread is rolled and the parts plated and gauged at the shoulder. Basis: Step face kept square through the route. |
|
Step face checked
The step face is checked for squareness to the axis, because a face that is off tips the shoulder in its bore when the thread tightens. Basis: Step face checked for squareness. |
First article in the bore
The first article is fitted into the customer bore and threaded into the far part, because the two fits are only proved together. Basis: First article fitted in the bore. |
Shi Shi Tong makes these metric precision shoulder screws by forming the truss head and shoulder with the step face square to the axis, then cutting the small thread and white zinc plating the finished parts. The first part of every run is measured on head, shoulder diameter and length, step face and thread before the batch continues.
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On metric precision shoulder screws the step face is where the part is decided. It is a narrow ring at the end of the shoulder, and it has to be cut square and clean in the same operation that sizes the shoulder; a step face that is slightly tapered lets the shoulder move under load, and the part that was a precision pivot becomes a loose one.
What decides whether these shoulder screws pass is the shoulder, the step face, the thread and the head. The inspection agreement covers those, and the criteria come from the drawing.
Shoulder and step on the projector |
Thread gauged after plating |
Hardness checked on the wire |
Coating proved by salt spray |
The shoulder is measured for diameter and roundness at several positions, the step face for squareness, and the thread is gauged after plating. The head is checked for diameter, height and face flatness, and the coating for thickness.
The first article is fitted into the customer bore and threaded into the far part. A stepped screw that measures correctly and binds when both fits are made is still a part that fails, and only the assembly shows it.
Every shipment of these shoulder 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 inspection records follow the criteria agreed on the drawing.
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 coating. The documents carry the drawing revision and the batch number, so a repeat order keeps the same shoulder tolerance and step geometry.
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 these shoulder screws the first article is fitted into the customer bore and threaded into the far part, because the two fits are only proved together. Buyers visit during the process to review samples.
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8,678+
customers served
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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 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 |
The shoulder bears and locates; the thread only pulls. A small thread fits a small tapped hole, which a thread the size of the shoulder would not.
It is the ring where the shoulder meets the thread, and it transfers the clamp from the thread into the shoulder.
Shoulder length for the bearing, and thread length from the shoulder end. Overall length alone does not define the part.
Yes, on the shoulder, the step and the thread. The parts are gauged after plating, or the shoulder is masked or sized for it.
A clearance fit sized to the bore. Too tight and it binds before the thread engages; too loose and the joint moves.
Shoulder diameter and tolerance, shoulder length, thread size and length, step face, head and the finish.
How a stepped shoulder screw project runs from drawing to repeat delivery:
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1
Send the drawing and the bore it fits
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→ |
2
Shoulder, thread and step agreed
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→ |
3
First article fitted in your bore
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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, thread size and length, head diameter and height, and the finish.
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Shoulder diameter
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Shoulder length
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Thread size
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Thread length
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Head diameter
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Finish
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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
