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:Small Countersunk Screws
Materials:Steel
Surface treatment:Blue zinc plated
Head Type:Countersunk flat head
Drive:Phillips cross recess
Thread:Coarse self tapping thread
Point:Pointed, per drawing
Forming:Cold heading and thread rolling
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10
We make small countersunk screws in steel with a blue zinc plate, a self tapping thread and a Phillips recess, quoted from M1 upward. The cone angle and pitch are agreed against your sheet or boss, and the first article is driven into your part to prove the head sits flush.
Watch the factory video·Email sst@szsst88.com
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.
Small countersunk screws are miniature screws with a cone-shaped head that sits flush in a matching countersink, used where the fixing must not stand above the surface. The part recorded here is steel with a blue zinc plate, with a self tapping thread and a Phillips recess, quoted from M1 upward.
Countersunk head. A cone that seats in the customer’s countersink so the surface stays flat.
Self tapping thread. A coarse thread that makes its own thread in a plastic boss or a thin sheet.
Phillips recess. A cross sized to the small head and driven with a standard bit.
They are used in miniature enclosures, instruments and small appliances, where a flush fixing has to make its own thread in a thin section of material. That combination is what separates them from a plain countersunk machine screw: the head is the same, but the thread does the work of an insert.
A countersunk self tapping screw puts two opposing actions into the same hole. The thread pulls material up and outward as it forms its own path, while the cone pushes the surface down as the head enters the countersink. On a thick metal part those two actions can coexist; on a thin plastic or sheet section they meet at the rim of the countersink, and that is where these small countersunk screws succeed or fail.
In a soft plastic the cone usually wins too late. The countersink is formed or moulded, and the material around it is thin. As the thread forms, it lifts material toward the surface; as the head seats, the cone presses back. The result is a compressed rim: the head sinks a little further than the drawing allows, or the rim lifts into a ring that shows around the head. Both are visible on a flush joint, and neither is a screw dimension alone.
In thin sheet the order is different. The cone has to be pressed into a metal countersink, and the self tapping thread cuts the hole below it. If the sheet is thin, the countersink is shallow, and a cone that is deeper than the sheet can take will stand the head off the surface or distort the sheet around the hole.
The coating adds a third effect. Blue zinc is softer than the base steel, and on a self tapping screw the plate is on the surface that does the cutting. Some of it is scraped off into the joint during driving, and what remains on the cone is a film between two surfaces that are meant to meet. On a small screw with a shallow countersink, that film is enough to change how flush the head sits.
All of this is why small countersunk screws are specified together with the part they go into. The head angle, the countersink depth, the sheet or boss thickness and the thread pitch form one joint, and the drawing for the screw is only half of it.
The part is quoted to the drawing with the head, the thread and the mating part stated separately. Custom lengths up to 2,000 mm, subject to DFM review after drawing submission. The quotation for small countersunk screws carries the head diameter and angle, the recess, the thread and pitch, the length under the head, and the sheet or boss thickness.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Countersunk cone | Diameter, angle and cone edge |
| Recess | Phillips | Depth and width |
| Thread | Self tapping, coarse | Diameter, pitch and point |
| Sheet | In the customer part | Thickness and countersink depth |
| Plate | Blue zinc | Thickness and coverage |
| Torque | Assembly torque | Stated for the material |
The cone angle is a pair with the customer countersink, and on a self tapping screw it is also a pair with the sheet thickness. A cone that is too deep for the sheet removes too much material around the hole, which is where a thin part tears first.
The thread pitch is chosen for the material rather than for the screw size. A pitch that suits a plastic boss is too coarse for a thin metal sheet, and a pitch that suits sheet tears the surface of a soft plastic.
The length under the head is measured to the underside of the cone, so it has to account for the countersink depth. A screw that is correct as a length but not as a length under the cone will bottom out in a blind boss.
Four properties decide small countersunk screws, and each one carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Countersunk head | Flush surface | Cone must match the countersink |
| Self tapping thread | No tapped hole | Loads the rim of the countersink |
| Blue zinc | Sacrificial protection | Soft plate smears while forming |
| Small head | Disappears in a small part | Little material around the recess |
The value is a fixing that is invisible and needs nothing behind it at all. On a miniature product both matter: there is no room for a nut, and a head that stands above the surface is the first thing a user feels.
The cost is that the flushness depends on the material. The screw is doing two jobs at the same hole, and the softer or thinner the part is, the more that shows in the finished surface. That is the price of combining two functions in one small part.
The recorded finish is blue zinc, a coloured sacrificial plate. On small countersunk screws it gives a bright finish and protection at low cost, and it is the usual choice for small appliance and electronics hardware.
| Option | How it protects | Effect on cone and thread | Typical use |
|---|---|---|---|
| Blue zinc | Sacrificial zinc | Soft plate smears while forming | Small appliance hardware |
| Clear zinc | Sacrificial zinc, thinner | Less smear; less protection | Indoor electronics |
| Zinc nickel | Higher corrosion resistance | Build on cone; re-checked | Damp and industrial |
| Black oxide | Conversion film, oiled | No measurable build | Dark mechanisms |
| Stainless, passivated | Passive film, no coating | No smear; no sacrificial layer | Wet and food areas |
On a self tapping screw the plate is a working surface. A soft plate is scraped away where the thread cuts, so the protection it gives is not uniform, and the part that matters is the cone and the head edge rather than the thread.
Where the joint sees moisture, the answer is not a thicker plate but a different base material. Zinc protects by being consumed, and on a small part there is very little of it to consume at an edge.
Three assemblies where a flush head and a self made thread are both required:
| Where it sits | The screw closes a cover onto a thin plastic boss where the outside surface must stay flat. |
| When it goes wrong | The head sits proud, or the rim of the countersink lifts into a ring. |
| Why it happens | The cone and the boss section are fighting at the same hole. |
| What we control | Cone angle and boss section agreed; first article driven into the real cover. |
| Where it sits | The screw holds a trim or a panel where the surface is touched and seen. |
| When it goes wrong | The plate wears through at the head edge, or the panel cracks at the countersink. |
| Why it happens | The plate is thin at an edge, and the panel is thin around the hole. |
| What we control | Plate coverage and cone depth checked; first article assembled on the panel. |
| Where it sits | The screw fixes a board or a bracket into a thin section where no tapped insert fits. |
| When it goes wrong | The thread strips in the boss, or the joint loosens after a few openings. |
| Why it happens | The pitch is too fine for the material, and there is no locking feature. |
| What we control | Pitch and boss hole agreed; first article assembled and re-opened. |
Four reasons that matter on a part where the head and the thread load the same hole, each tied to something the drawing or the first article proves. All four show in the sample.
|
Cone, pitch and sheet agreed
The quotation asks for the countersink and the sheet or boss thickness, because on small countersunk screws those decide whether the head sits flush. Basis: Cone, pitch and sheet agreed. |
Cone and thread made as a pair
The cone is formed with the head and the thread made to the pitch the material needs, not to a catalogue default. Basis: Cone and thread as a pair. |
|
Driven into your part
The first article is driven into the customer part at the intended torque, because the rim only shows in the joint. Basis: Rim proved in the part. |
Same seat on repeat runs
Cone angle, pitch and plate are recorded with the drawing revision, so a repeat batch seats the same way. Basis: Same seat across orders. |
These screws are cold headed from steel wire, with the countersunk head formed, the point formed, the thread rolled and the parts then blue zinc plated. The first piece of every run is measured on head diameter and cone angle, recess depth, thread diameter and pitch, point form and plate thickness.
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The cone is formed in the heading die, so its angle comes from the die rather than from a later cut. That is what keeps the cone concentric with the thread: on a small countersunk screw a cone that is off-axis shows as a head that sits at an angle in the countersink, with one side bearing and the other standing proud.
The thread is rolled after heading, so the material at the start of the thread is worked rather than cut. On a self tapping screw that matters, because the start is what enters the boss first, and a torn start cuts a poor thread in the plastic.
Plating comes last and is checked on the cone. A heavy blue zinc layer on a small cone changes the seating depth, which is why the plate thickness is a control point rather than a description.
What decides whether small countersunk screws pass is the cone, the thread start and the plate. The inspection agreement covers those, and the criteria come from the drawing.
Cone and head on the projector |
Thread gauged |
Core hardness checked |
Salt-spray testing of the blue zinc |
The cone is measured for angle and for concentricity with the thread, and the edge between the cone and the head is checked for a burr. On a flush joint a burr at that edge is a ring that shows in the finished surface.
The thread start is checked for torn material and the point for form. A start that is ragged will not enter a small boss cleanly, and the material it displaces ends up around the countersink.
The plate is checked for thickness and coverage, and a sample goes into the salt-spray chamber. On a small part the edges are where the plate runs thin, and the head edge is the edge that is seen.
Every batch of small countersunk screws is traceable to the wire 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 cone and the thread start, and the plating report. The records carry the drawing revision and the batch number, so a repeat order of small countersunk screws seats 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 small countersunk screw the first article is driven into the customer part, because the rim and the flushness only exist in the joint. 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 heading 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 |
The countersink compresses as the thread forms. The material around it is thin, and the cone cannot keep the surface flat on its own.
Yes, and that is the more common failure on soft plastics. Over-driving crushes the rim and the head sinks.
Blue zinc is soft, and the thread is the cutting surface. Some plate is scraped off during driving, which is normal on a self tapping screw.
On a thin sheet it does. A cone deeper than the sheet can take distorts the sheet or stands the head off.
Only a few times. Each re-drive works the plastic or the sheet again, and the formed thread gets looser.
Head diameter and cone angle, recess, thread and pitch, length under the cone, plate specification, and the sheet or boss thickness.
How a small countersunk screw project runs from drawing to repeat delivery:
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1
Send the drawing and the sheet or boss
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→ |
2
Cone angle and pitch agreed
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→ |
3
First article driven into 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 head diameter and cone angle, the recess, thread and pitch, length under the cone, plate specification, and the sheet or boss thickness.
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Head diameter
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Cone angle
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Recess
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Thread pitch
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Length
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Section thickness
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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
