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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:Reduced Head Countersunk Screw, 3mm Countersunk Machine Screws
Materials:Carbon Steel
Surface treatment:Blue Zinc Plated
Head Type:Reduced flat (countersunk)
Drive:Phillips cross recess
Thread:Machine thread
Point:Plain, chamfered
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10
We make reduced head countersunk screws in carbon steel with a blue zinc finish, quoting them from M1 to M10 with lengths made to the drawing. The reduced head diameter and the countersink are agreed together, and the first article is seated in your own 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.
A reduced head countersunk screw is a countersunk screw whose head diameter is smaller than the standard for its thread, so it seats in a smaller countersink. The part recorded here is carbon steel with a blue zinc finish, quoted from M1 to M10 with lengths made to the drawing.
Reduced head. A cone cut to a smaller diameter than the standard head, so the screw fits where the seat is narrow.
Countersunk. A conical underside at 90 degrees that seats in the countersink and finishes level with the surface.
Cross recess. Four tapered arms driven by a matching bit, sized as a PH number.
Blue zinc. A thin electroplated zinc with a bright passivate, common on small carbon steel parts.
They are used where the edge distance is tight: instrument and electronic enclosures, small brackets, hinges on thin sections, and any panel where a standard countersunk head would break through the chamfer or leave too little material around the hole.
A standard countersunk head is sized so that the cone, the bearing band and the head diameter all balance for a given thread, and a reduced head countersunk screw deliberately breaks that balance. Reducing the diameter takes that balance apart in a specific way: the cone angle stays the same, so the cone becomes shorter and the bearing band narrower, while the head height above the cone does not change.
The first consequence is pressure. Clamp load divided by bearing area gives the pressure on the seat, and a smaller head has less area, so the same torque presses harder into the material around the countersink. On steel that is usually acceptable; on aluminium, brass or a thin sheet the seat deforms and the head sinks slightly, which shows as a head that is level but surrounded by a raised ring.
The second consequence is favourable and often overlooked. Because the head height stays while the diameter shrinks, the recess has the same depth as a standard part and the bit engages fully. A reduced head screw therefore often drives better than a standard one of the same thread, which is the opposite of what the smaller head suggests.
The third is edge distance. That is normally the reason for choosing the part: on a narrow flange, the standard head would break through the chamfer or leave a wall too thin to carry the load. Reducing the diameter keeps the seat inside the material, and the joint stays inside its own geometry rather than at its edge.
What all three add up to is a joint that has to be specified by the seat, not only by the screw. The countersink diameter, its depth and the distance to the nearest edge belong on the mating drawing, because a reduced head screw has less margin for a seat that is slightly off.
The recorded range is M1 to M10, with lengths made to the drawing. Custom lengths up to 2,000 mm are subject to the drawing submission and DFM review. The quotation for reduced head countersunk screws carries the reduced head diameter, the countersink angle, the head height, the PH size and recess depth, the thread pitch and the overall length.
| Item | How it is defined | What we control |
|---|---|---|
| Head diameter | Reduced, smaller than standard | Diameter and cone concentricity |
| Cone | Countersink angle, usually 90 degrees | Angle and cone length |
| Head height | Kept at standard for the thread | Height and recess depth |
| Recess | Phillips, PH size per diameter | Arm depth and floor thickness |
| Thread | Machine thread in carbon steel | Pitch, length and start position |
| Length | Overall, head included | Length tolerance and thread start |
The reduced diameter has to be stated as a dimension, not as a description. “Reduced head” covers a range of diameters between the standard head and a small head, and two suppliers can both comply while delivering parts that need different countersinks.
Head height is measured because it should stay at the standard value. A supplier that reduces the height along with the diameter has changed the recess depth, and the part will no longer take the bit as the drawing assumes.
Edge distance is measured on the mating part rather than on the screw, and it is the number that usually decides whether the joint works. A reduced head is chosen for that reason, so the seat and the edge are reviewed together on the first article.
Four properties decide reduced head countersunk screws, and each one carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Smaller diameter | Fits where the seat is narrow | Higher pressure on the seat |
| Standard head height | Full-depth recess and good drive | Head looks larger in proportion |
| Cone seat | Flush finish | Needs a matching, smaller countersink |
| Blue zinc | Bright sacrificial protection | Thin coating at a sheared rim |
The value is that a joint which would otherwise need a different design becomes possible with a standard thread, and that is what a reduced head countersunk screw is bought for. Instead of thickening the flange or moving the hole inboard, the fixing is reduced to fit what the part already is, and the assembly keeps its dimensions.
The cost is margin. The bearing band is narrower, so the seat has to be right, the material has to be able to take the pressure, and the countersink has to be cut to the diameter the drawing states rather than to the standard one.
The recorded finish is blue zinc, electroplated with a bright passivate. It protects by sacrificial action and it is the usual finish for small carbon steel parts that are not expected to survive weather.
| Option | How it protects | Effect on head and recess | Typical use |
|---|---|---|---|
| Blue zinc | Thin sacrificial zinc | Thin at the rim; bright tone | Instrument and enclosure work |
| Clear zinc | Trivalent zinc, bright | Same; lighter | General indoor work |
| Black zinc | Zinc with a dark passivate | Dark head on dark panels | Equipment housings |
| Nickel plated | Hard bright barrier | Build on the cone; seating changes | Visible bright fixings |
| Stainless, passivated | Passive film, no coating | No build; no coating to shear | Wet and visible joints |
On a reduced head the rim is closer to the recess, so the thinnest part of the coating is also the most visible part of the head. A part that looks well plated on the face can show a bare arc at the rim, and on a visible panel that reads as a defective fixing.
Where the joint is damp, stainless is the honest choice. A thin zinc layer at a sheared rim is not a protection strategy, it is a delay.
Three settings where the edge distance decides the design:
| Where it sits | The screw closes a case where the wall is thin and a standard head would break out through the chamfer. |
| When it goes wrong | The head breaks the edge, or the wall cracks at the countersink during assembly. |
| Why it happens | The wall is thin, the seat is near an edge, and the fixing is repeated. |
| What we control | Reduced diameter and seat checked; first article fitted in the case. |
| Where it sits | The screw fixes a hinge leaf where the flange is narrow and the countersink sits close to a fold. |
| When it goes wrong | The countersink runs into the fold and the head sits on one side only. |
| Why it happens | The part is small, formed, and assembled by hand. |
| What we control | Seat and edge distance checked; first article assembled and cycled. |
| Where it sits | The screw closes a panel that already has a small chamfer and cannot be re-machined. |
| When it goes wrong | A standard head is forced into the seat and stands proud around the rim. |
| Why it happens | The existing part cannot change, and the fixing has to match it. |
| What we control | Diameter matched to the existing seat; first article tried in the panel. |
Four reasons that matter on a head with less margin, each tied to something the drawing has to prove:
|
Reduced diameter stated as a number
The head diameter is written as a dimension rather than described, because reduced head covers a range and the countersink has to match the exact value. Basis: Diameter stated, not described. |
Headed, recessed, threaded, plated
The cone and the head are formed in one stroke with the height kept at standard, the recess cut, the thread rolled and the batch plated. Basis: One route with standard height. |
|
Diameter, height and recess measured
Head diameter, cone angle, head height and recess depth are measured together, because a reduced diameter with a reduced height has quietly become a different part. Basis: All four measured together. |
Same head, same seat
The heading punch and the recess tool are recorded with the drawing revision, so a repeat order drops into the same countersink. Basis: Same seat across orders. |
These screws are headed on single-die machines that form the cone and the reduced head in one stroke, cut with the cross recess, thread rolled and zinc plated as a batch. The first part of every run is measured on head diameter, cone angle, head height, recess depth, thread and length.
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Forming the head of a reduced head countersunk screw is a matter of controlling where the metal stops flowing outwards. The punch has to leave a cone whose diameter is smaller than the standard head while the height above the cone stays the same, and those two requirements pull against each other: pushing the metal less far outwards leaves it stacked in the centre, and the head grows taller unless the punch is shaped for it.
The recess is cut after the head is formed and is the easiest thing to get subtly wrong on this part. Because the head diameter is smaller, a recess that is correct in size sits proportionally closer to the rim, and any drift in the punch position shows as a thin wall on one side. That is measured on the first article rather than sampled later.
Plating is checked on the rim and on the cone as well as on the face. On a reduced head the rim is short and close to the recess, so the two thinnest areas of the coating are next to each other and both are visible when the part is seated.
What decides whether reduced head countersunk screws pass is the head diameter, the cone, the recess and the thread. The inspection agreement covers those, and the criteria come from the drawing.
Diameter and cone on the projector |
Thread and start checked |
Core hardness checked |
Salt-spray testing of the plated head |
Head diameter and cone angle are measured first, because they are what the seat has to match, and head height is read at the same time to confirm it stayed at the standard value. The recess is measured and proved with the production bit at the line torque.
Bearing is proved functionally. A sample from every batch is seated in a countersunk test plate cut to the reduced diameter and checked for rocking, for a gap under the rim and for sinking into the seat. On a smaller head any of those three shows earlier than on a standard part.
A sample is also driven into the customer’s part and removed, which is where a seat that is slightly off centre shows as a bright arc on one side of the cone, and on a reduced head countersunk screw that arc is the difference between a flush fixing and a loose one.
Every batch 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 inspection records follow the criteria agreed on 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 for the dimensions on the drawing including the reduced head diameter, and the plating and RoHS reports. The documents carry the drawing revision and the batch number, so a repeat order of reduced head countersunk screws fits the same seat.
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 reduced head the first article is seated in the customer part, because a small seat has no margin for a slightly different cone. Buyers visit during the process to review samples.
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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 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 |
To fit a smaller countersink, usually because the hole is close to an edge and a standard head would break out or leave too little material.
The thread is the same; the bearing area is smaller, so the pressure on the seat is higher. On soft or thin material that is the limiting factor.
It should not. Keeping the standard height preserves the recess depth and the drive, even though the diameter is smaller.
Only in a countersink cut to the reduced diameter. In a standard countersink it drops in and the head finishes below the surface.
On steel usually not. On aluminium, brass or thin sheet the seat can deform, so the torque is set for the seat rather than for the thread.
Reduced head diameter, countersink angle and depth, head height, PH size, thread pitch and overall length.
How a reduced head screw project runs from drawing to repeat delivery:
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1
Send the drawing and the countersink size
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→ |
2
Reduced diameter and angle agreed
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→ |
3
First article seated 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 reduced head diameter, countersink angle and depth, head height, PH size, thread pitch and overall length.
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Head diameter
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Cone angle
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Head height
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PH size
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Thread pitch
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Length
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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
