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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:Csk Self Tapping Screw
Materials:Steel
Surface treatment:Blue Zinc Plated
Head Type:Flat Countersunk Head
Drive:Phillips Cross
Thread:Self Tapping Thread
Point:Sharp
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:682
We make csk self tapping screws in blue zinc plated carbon steel with a countersunk head, a sharp point and a Phillips recess, quoting them from M1 to M14. Head, cone, thread and coating thickness come from your drawing, and the first article is driven into your own sheet.
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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.
A csk self tapping screw is a self-tapping screw with a countersunk head: the thread forms its own thread in a pilot hole, the sharp point starts it, and the cone under the head finishes flush with the panel. This family is made in carbon steel with a blue zinc plate, a flat countersunk head and a Phillips recess, quoted from M1 to M14 with Number 682 and filed under the self-tapping group.
Countersunk head. A 90-degree cone under a flat top face, so the head sits inside the material instead of on it.
Self-tapping thread. A coarse thread with a sharp crest, sized to cut its own thread in a pilot hole rather than to run in a pre-cut one.
Sharp point. A tapered end that finds the hole and starts the thread on the first turn.
Blue zinc. An electroplated zinc deposit with a clear-blue chromate film: thin, bright, sacrificial, and about as cheap as a coating gets.
A coated self-tapping screw spends its working life scraping its own coating off. The thread cuts into the sheet, the crest is what does the cutting, and the zinc on that crest goes first. What is left is a joint formed by bare steel pressed into bare steel, inside a closed assembly where nobody looks until it rusts.
That is the honest way to read a csk self tapping screw: the coating protects the screw in the box and around the joint, but not at the two places where the joint is actually made. The crest of the thread loses its zinc as it cuts, and the cone under the head loses it wherever the seat is disturbed — on the first turn, or on the rework that follows a stripped hole.
Zinc is the right coating for that job anyway, because it works as a sacrificial anode. Where the coating is scratched at the crest, the surrounding zinc still protects the steel beside it, so the joint does not rust at the scrape; it rusts at the far edge of the sacrificial zone, which is a much slower story. A barrier coating such as nickel would fail at the same place without that margin.
The countersunk head adds one specific wear point. The cone is in full contact with the panel from the moment the head seats, and every cycle of the joint rubs the coating on the cone against the sheet. In a panel that is opened and closed, that is where the first red rust appears on a blue zinc screw, and it appears on the underside where it cannot be seen.
Electroplating also has a manufacturing consequence on a hardened self-tapping screw. The plating process charges the surface with hydrogen, and a case-hardened part can become brittle enough to snap at the head fillet after the batch is plated. Where the part is hardened, the process includes the post-plating bake that drives the hydrogen out, and the drawing should say whether it is required.
The recorded range is M1 to M14, covering M1, M2, M3, M4, M5, M6, M7, M8, M9, M10 and M14. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. On a coated csk self tapping screw the coating has to be quoted with the size, because a deposit that is negligible on an M8 is a measurable fraction of a head and a recess on an M2.
| Item | How it is defined | What we control |
|---|---|---|
| Head | Countersunk, 90-degree cone | Head diameter, height and cone angle |
| Recess | Phillips cross | Recess size and depth after plating |
| Thread | Self-tapping, coarse pitch | Pitch and major diameter, gauged |
| Point | Sharp, tapered | Point angle and thread start |
| Finish | Blue zinc, clear-blue chromate | Deposit thickness and adhesion |
| Length | Under the head to the point | Measured on the shop plate |
Length is measured from under the head, because the head is inside the panel and the thread length is what has to pass through the material. On a flush fixing the head diameter and the cone angle sit next to the length for a reason: a screw of the right length with the wrong cone still will not seat.
Coating build is checked after plating, not before. A zinc deposit thick enough to matter will narrow the recess and thicken the thread crest, and both change the way the screw behaves in the customer’s panel. Where a batch is plated in a different barrel load and comes out slightly thicker, the difference shows up at assembly rather than in the dimensional report.
Three features define this part: the sharp point, the countersunk cone and the blue zinc. The first starts the thread, the second buries the head, and the third is the only thing standing between a steel screw and a rusty joint.
| Feature | What it gives | What it costs |
|---|---|---|
| Sharp point | Starts without a fixture | Needs a pilot hole of the right size |
| Countersunk cone | Flush surface, self-centring | Needs a matching countersink in the panel |
| Coarse self-tapping thread | Holds in thin sheet | Strips if over-driven |
| Phillips recess | Common driver, defined cam-out | Cam-out damages the coating first |
| Blue zinc | Sacrificial protection, low cost | Scraped at the crest as it cuts |
The sharp point is what makes the part usable in hand assembly. It finds the hole, starts the thread, and lets the operator work without a jig — which is also why the same screw in a machine-fed station with a blunt point behaves differently and needs a different set-up.
The coat is the part that wears first at the drive. A driver that cams out of the recess takes the chromate film with it, and the recess becomes the wettest, least ventilated part of the joint. That is why a cam-out is worth avoiding on a coated screw even when the recess survives.
The recorded finish is blue zinc, an electroplated zinc deposit passivated with a clear-blue chromate. It is thin, bright and sacrificial, and it is the default finish wherever a steel screw has to look clean and last longer than bare steel indoors. It is not a coating for salt, and it is not a coating for a joint that will be opened repeatedly.
| Option | How it protects | Effect on head and thread | Typical use |
|---|---|---|---|
| Blue zinc | Sacrificial zinc, clear-blue chromate | Thin; fit re-checked after plating | Indoor panels and appliances |
| White zinc | Sacrificial zinc, trivalent | Thin; more uniform appearance | Indoor, RoHS-driven work |
| Black zinc | Sacrificial zinc, dark | Thin; marks dark panels less | Dark equipment and trim |
| Nickel plated | Barrier deposit, bright | Decorative; fails at a scratch | Visible indoor panels |
| Dacromet | Zinc-aluminium flake layer | Thicker film; fit re-checked | Outdoor and damp steel |
The choice between blue and white zinc is usually made on appearance and specification rather than corrosion. Blue chromate gives the bluish-bright look that reads as hardware; trivalent white zinc is the finish that fits the common RoHS limits and looks slightly warmer. Both are a few microns of zinc over steel and both behave the same way in a joint.
Where the joint will see real moisture, none of the bright zinc options is the answer and the stainless version of the same screw is. The geometry does not change — countersunk head, coarse thread, sharp point — only the material and the way it fails.
Three assemblies where a csk self tapping screw is the fixing:
| Where it sits | The screw closes a panel in thin sheet where the fixings are many, the surface has to stay flat and the driver is a standard power tool. |
| When it goes wrong | An over-driven screw strips the sheet, and the zinc scraped at the crest leaves bare steel inside a closed box. |
| Why it happens | The panel is thin, the fixing is repeated, and the head has to disappear. |
| What we control | Point and thread checked, pilot hole agreed against the sheet thickness. |
| Where it sits | The screw fixes a cover or a duct panel where the part has to look bright and flush and cost little enough to be used in thousands. |
| When it goes wrong | A cam-out takes the chromate off the recess, and the first rust appears at the head rather than in the panel. |
| Why it happens | The surface is visible, the volume is high, and the assembly is by hand. |
| What we control | Plating thickness and adhesion checked, recess driven after plating. |
| Where it sits | The screw fixes a cover or a plate where the head must be flush and the wall is thin enough that the countersink matters. |
| When it goes wrong | A screw that is too long breaks through the back of the box, and a stripped thread leaves a lid that will not close. |
| Why it happens | The enclosure is thin, the fixing is one-sided, and the part is installed on site. |
| What we control | Point, thread and length checked, first article fitted into the box. |
Four reasons that matter on a coated self-tapping screw, each tied to what the drawing has to prove:
|
Coating and pilot hole reviewed together
The plating thickness, the pilot hole and the sheet thickness are reviewed as one set, because the deposit enters both the thread fit and the flush seat. Basis: Coating, hole and sheet reviewed together. |
Head, thread and plate in one route
The countersunk head and the Phillips recess are formed in the heading stroke, the self-tapping thread is rolled and the parts are zinc plated and passivated in the same route. Basis: One route from wire to plated screw. |
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Driven after plating, not before
The recess and thread are checked and driven after plating, because the condition the customer receives is the plated part, not the bare one. Basis: First article driven after plating. |
First article fixes the setting
The first article fixes the wire heat, the point die and the plating; repeat orders are compared against that record. Basis: First article signed off before the batch is released. |
Shi Shi Tong forms these csk self tapping screws from carbon steel wire on single-die headers that cut the countersunk head and the Phillips recess in one stroke, rolls the self-tapping thread, forms the sharp point and sends the parts to zinc plating and passivation. The first part of every run is measured on the head and cone, driven into a sheet of the customer’s thickness and checked in a thread gauge before the batch continues.
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The two tools that decide the batch are the cone die and the point die. A worn cone leaves a face that seats on the rim of the countersink rather than on the whole cone, and a blunt point makes the operator push, which domes the sheet. Both are checked at the start of the run, because neither shows up in a dimensional report taken at the end.
What decides whether csk self tapping screws pass is the cone, the thread, the point and the coating. The inspection agreement covers those, and the criteria come from the drawing.
Cone and thread on the projector |
Thread gauged per batch |
Hardness checked against the grade |
Salt-spray testing of the plate |
Every csk self tapping screw is checked for head diameter, head height and cone angle on the first article, then driven into a test sheet and pulled to the strip point. The thread is gauged per batch, the point is checked for angle and start, and the recess is driven with the production bit after plating.
The coating is checked for thickness, adhesion and appearance, and the salt-spray sample is run where the customer’s environment asks for it. Adhesion matters more than thickness on a self-tapping screw: a deposit that flakes at the crest as the thread cuts leaves a bare patch that a thickness reading never sees.
Every shipment of csk self tapping 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 plating record is kept with the inspection file.
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 plating. The documents carry the drawing revision and the batch number, so the paperwork can be matched to the parts.
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 self-tapping part the first article is driven into the customer’s own sheet, because the joint is the function. Buyers visit during the process to review samples and to see how the heads and points are formed.
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8,678+
customers served
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87%
of orders from repeat customers
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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 |
Countersunk. The head is a cone under a flat top so it finishes flush; the thread is still self-tapping, cutting its own thread in a drilled or punched hole.
At the crest of the thread, yes — that is where the screw cuts. Zinc around the scrape still protects the steel beside it, which is why a sacrificial coating works better here than a barrier one.
Between the root and the crest of the thread, sized to the sheet thickness and material. It decides whether the joint holds or strips, so it belongs on the drawing.
The cone under a countersunk head is in permanent contact with the panel and loses its chromate where the joint moves. Rust at the joint, not at the recess, is the sign of that contact wear.
For occasional exposure, it is a starting point. For permanent damp or salt, use a stainless screw or a flake coating; bright zinc is a few microns and will not survive those conditions.
Thread size and length, point form, head diameter, cone angle, recess type, the sheet material and thickness, and the coating with its thickness.
How a csk self tapping screw project runs from drawing to repeat delivery:
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1
Send the drawing and the panel it goes into
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→ |
2
Pilot hole, head and coating agreed
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→ |
3
First article driven into your sheet
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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 thread size and length, the point form, the head diameter and cone angle, the recess type, and the material and thickness of the sheet.
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Thread size
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Length
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Point form
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Head diameter
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Cone angle
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Coating
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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
