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+86 13143444311
Email：sst@szsst88.com
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Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Type:Shoulder Screws Metric Pan Washer Head Phillips
Materials:Stainless Steel
Surface treatment:Plain
Head Type:Pan Washer Head
Drive:Phillips (cross)
Thread:Machine thread, partial
Point:Blunt
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:156
We make these metric shoulder screws in passivated A2 stainless, with a pan washer head, a Phillips recess, a plain shoulder and a partial thread, quoted from M1 to M14. Washer diameter, shoulder tolerance and length, thread position and grade come from your drawing, and the first article is fitted in your 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.
These metric shoulder screws are small stainless fasteners with a pan washer head, a Phillips recess, a plain shoulder and a partial thread at the end, quoted from M1 to M14 with Number 156. The washer face under the head spreads the clamp load, the shoulder runs in a bore as a bearing, and the thread only exists where the screw enters the tapped part.
Pan washer head. A pan head with an integral washer face, so the bearing diameter is larger than the head dome and no separate washer is needed.
Shoulder. A plain cylindrical section between head and thread that runs in a bore and carries the radial load.
Partial thread. The thread starts part way down, leaving the shoulder as a plain shank for most of the length.
Passivated stainless. A2 grade, uncoated, so the shoulder and the thread are as made.
Metric shoulder screws are specified in millimetres as a shoulder diameter with a tolerance, a shoulder length and a thread size, and the part is judged by the fit in its bore rather than by its thread class. That is why the shoulder numbers carry tolerances and the thread carries a gauge.
On these metric shoulder screws sizing hides two separate load paths. The washer face under the head takes the clamp force and spreads it over a ring wide enough for a soft or thin panel. The shoulder takes the radial load in the bore, like a small shaft. The thread at the end does neither; it only generates the preload that holds the other two in place.
That separation matters when a joint is redesigned. A customer who needs more clamp adds torque, which loads the washer face and the thread; a customer who needs less play changes the bore, which changes the shoulder fit. Neither change affects the other, and a drawing that treats the part as one threaded fastener makes both harder to control.
The integral washer is what makes the head usable on plastic and thin sheet. A plain pan head has a bearing ring of the head diameter; the washer face adds a flat annulus that extends past the dome, so the same clamp force is spread over more area and the panel does not dish. It also means there is no separate washer to lose during service.
The partial thread follows from the shoulder. There is no reason to thread the section that has to run in a bore, and a thread carried through it would cut the bore and destroy the fit. The thread starts just below the shoulder, and its length is set by the depth of the tapped part rather than by the screw’s overall length.
The Phillips recess is the torque limit on the assembly. A pan washer head has a shallow dome above the washer face, and a cross cut into it engages a short length of bit; the joint torque has to be one the recess will take cold, or the cross rounds before the washer face has done its work.
Where the joint is opened often, that recess is what wears. Stainless holds it better than a plated head because there is no soft deposit to rub away, but the arm of the cross is thin and a worn PH0 bit will ream it in a few dozen assemblies.
The recorded range is M1 to M14, with the metric shoulder sizes M2, M2.5, M3, M4, M5 and M6 covering most small mechanisms. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. For these metric shoulder screws dimensions are quoted as shoulder diameter and tolerance, shoulder length, head diameter, thread size and thread length.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Pan washer head | Washer diameter, head height and face flatness |
| Shoulder | Plain bearing section | Diameter, tolerance and surface finish |
| Shoulder length | Bearing length | Length tolerance and face squareness |
| Thread | Partial machine thread | Thread size, length and gauging |
| Recess | Phillips cross | Recess size and depth |
| Material | A2 stainless | Grade and heat number on the certificate |
| Finish | Passivated | Surface condition and film |
On metric shoulder screws the sizes are nominal but the fit is not. A 3 mm shoulder is made slightly under a 3 mm reamed bore; the tolerance on the shoulder is what sets the play, and it belongs on the drawing with the bore it runs in.
Thread length should be quoted from the end of the shoulder, not from the tip. A partial thread placed by overall length will move when the shoulder length changes, and the screw will either not engage enough threads or bottom in the tapped part.
Three features define the part: the washer face, the shoulder and the partial thread. The first spreads the clamp on the part, the second bears the radial load, and the third is deliberately kept away from the first two.
| Feature | What it gives | What it costs |
|---|---|---|
| Washer face | Clamp spread without a separate washer | Larger head diameter to clear |
| Shoulder | A bearing journal in a small part | Diameter and finish must be held |
| Partial thread | Plain shank where the bore runs | Thread length must be placed |
| Phillips recess | Standard drive on a low head | Cam-out and recess wear |
| Passivated A2 | No build on shoulder or thread | Softer than steel; galls dry |
The washer face is the practical reason for the head form. It lets a small stainless screw clamp a moulded plastic boss or a thin panel without a washer, and it keeps doing that after several services because there is nothing to lose.
The cost is head diameter. A pan washer head needs clearance around the hole, and in a tight pocket the plain pan head or a low profile head is the only one that fits.
The recorded finish is passivation on bare A2 stainless. For these metric shoulder screws that is the right answer because both functional surfaces are bare metal: a coating would change the shoulder diameter and the thread fit, and no decorative deposit is worth losing the bore fit for.
| Option | How it protects | Effect on shoulder and thread | Typical use |
|---|---|---|---|
| A2 stainless, passivated | Passive chromium oxide film | None; as made | General mechanisms |
| A4 stainless, passivated | Passive film with molybdenum | None; as made | Marine and medical |
| Steel, nickel plated | Hard barrier deposit | Build on both; shoulder masked or sized | Indoor machine parts |
| Steel, black oxide | Conversion film, oiled | No measurable build | Internal mechanisms |
| Brass, plain | No coating needed | Softer shoulder; wears | Electrical and decorative |
For metric shoulder screws the stainless choice is also the choice that avoids a plating conversation. There is no deposit to allow for on the shoulder, so the diameter the drawing gives is the diameter the customer measures, and the fit in the bore is the same on the first order and the tenth.
Where the joint runs in a stainless bore at speed, a dry-film lubricant keeps the shoulder from galling. Passivation is not a lubricant, and stainless on stainless without one will pick up on the bearing surface.
Three assemblies where these metric shoulder screws are the fixing:
| Where it sits | The screw pulls a cover down onto a boss where the head has to spread load without a washer and the shoulder locates the cover. |
| When it goes wrong | A plain pan head dishes the boss, and a thread run into the shoulder cuts the locating bore. |
| Why it happens | The boss is plastic, the panel is thin, and the joint is serviced. |
| What we control | Washer diameter and shoulder length checked; first article fitted in the boss. |
| Where it sits | The screw pivots a lever or a link where the shoulder is the bearing and the head clamps the outer plate. |
| When it goes wrong | Shoulder play makes the linkage rattle, and thread wear makes the pivot loose. |
| Why it happens | The joint rotates, the bore is small, and the fit sets the play. |
| What we control | Shoulder diameter tolerance held; first article moved through its travel. |
| Where it sits | The screw fixes a faceplate where the washer face gives a clean bearing ring and the shoulder sets the stand-off from the chassis. |
| When it goes wrong | An over-long shoulder leaves the plate standing off, and a short one lets the plate move. |
| Why it happens | The joint sets a distance, the plate is thin, and appearance is specified. |
| What we control | Shoulder length matched to the stack; head and washer face checked. |
Four reasons that matter on a washer-head pivot, each tied to what the drawing has to prove:
|
Washer, shoulder and thread agreed
The washer diameter, shoulder tolerance, shoulder length and partial thread are agreed as one set, because on these metric shoulder screws the three carry different loads. Basis: Washer, shoulder and thread agreed. |
Headed, threaded, passivated in one route
The washer head and recess are formed, the shoulder is sized and the partial thread is rolled in one route before passivation. Basis: One route from wire to passivated screw. |
|
Shoulder checked for the bore
The shoulder is measured at several positions and the thread position checked from the shoulder end, because that is where the assembly feels it. Basis: Shoulder and thread position checked. |
First article fitted in the boss
The first article is fitted into the customer boss or bore and the fit recorded, so a repeat order is compared with the joint that worked. Basis: First article fitted in the boss. |
Shi Shi Tong forms these metric shoulder screws on single-die headers that form the pan washer head and cut the Phillips recess in one stroke, then sizes the shoulder, rolls the partial thread and passivates the finished screws. The first part of every run is measured on washer diameter, head height, shoulder diameter, shoulder length and thread position before the batch continues.
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The washer face is where a headed part is harder to make than a plain pan head. The punch has to form a dome and a flat annulus in the same stroke, and the corner between them has to be full; a soft corner leaves a radius that holds the washer face off the panel, and the whole point of the extra diameter is lost.
What decides whether these metric shoulder screws pass is the washer diameter and face, the shoulder diameter and length, the thread position and the recess. The inspection agreement covers those, and the criteria come from the drawing.
Head and shoulder on the projector |
Thread gauged per batch |
Hardness checked on the wire |
Salt-spray testing of the grade |
On metric shoulder screws the washer face is checked for diameter and flatness, the head for height, the shoulder for diameter and roundness, and the thread for position from the shoulder end. The recess is checked for depth, and the thread is gauged per batch.
The first article is driven into the customer’s boss and the cover checked for stand-off and flatness. That is the assembly check these parts are bought for, and it catches a shoulder length that is right on the drawing and wrong in the stack.
Every shipment of these metric shoulder screws is traceable to the wire it was made from and to the passivation 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 grade. The documents carry the drawing revision and the batch number, so a repeat order is made to the same shoulder tolerance and thread position that were approved.
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 metric shoulder screws the first article is fitted into the customer boss, because the fit and the stand-off are the function. Buyers visit during the process to review samples and to see how the heads are formed.
|
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 headers and the passivation 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 |
It spreads the clamp load over a wider ring than a plain pan head, so a thin panel or plastic boss does not dish. No separate washer is needed.
The plain shoulder has to run in a bore. A thread carried through it would cut the bore and destroy the fit.
On the shoulder, not overall. The shoulder length is what the assembly feels, and the thread length is quoted from the shoulder end.
Usually a 4 mm shoulder with an M3 thread, so the thread passes through the bore. The drawing sets the pairing.
A clearance fit sized to the bore and to the allowed play. Too tight seizes, too loose lets the linkage rattle.
Washer diameter, head height, shoulder diameter and tolerance, shoulder length, thread size and length, recess and the grade.
How a washer-head shoulder screw project runs from drawing to repeat delivery:
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1
Send the drawing and the boss or bore
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→ |
2
Washer, shoulder and thread agreed
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→ |
3
First article fitted in your part
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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 washer diameter, head height, shoulder diameter and tolerance, shoulder length, thread size and length, and the grade.
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Washer diameter
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Head height
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Shoulder diameter
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Shoulder length
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Thread
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Grade
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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
