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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:low profile socket head cap screw
Materials:Stainless steel
Surface treatment:Plain
Head Type:PF. Head
Drive:Hexagon socket (Allen)
Thread:Metric machine thread
Point:Plain, chamfered
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10 M14
Number:236
We make low profile socket head cap screws in plain A2 stainless with a PF low head and a hexagon socket, quoting them from M1 to M14. Head height, socket depth, floor thickness and thread come from your drawing, and the first article is fitted under the cover it has to clear.
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.
A low profile socket head cap screw is a machine screw whose head is shorter than a standard cap head while keeping the same cylindrical form and the same internal hexagon drive. These are plain A2 stainless, quoted from M1 to M14 with Number 236, made to the drawing with a PF (low, flat-topped) head.
Low PF head. A cylindrical head with a flat top and a reduced height, so it takes less axial room than a standard cap head.
Hexagon socket. The drive sits inside the head, and its depth is limited by the head height above it.
Machine thread. A uniform metric thread for a tapped hole, a nut or a threaded insert.
Plain stainless. A2 grade, passivated and uncoated, so the socket and the bearing face are as formed.
Low profile socket head cap screws are chosen when the head has to disappear into a shallow space: inside a cover that closes onto a frame, next to a printed circuit board, behind a panel that sits a few tenths above the surface. The head loses height, not diameter, so the clamp face stays wide and the drive stays inside the head.
A cap head is a cylinder with a hexagon cut into it. The wall around the hexagon and the material between the bottom of the socket and the bearing face both come out of the same head height, so the low head does not just look shorter: it takes material away from the two places the drive depends on.
The first consequence is socket depth. A key needs a minimum engagement to transmit torque without twisting, and a shallow socket reduces that engagement. Below a certain depth the key starts to load the top edges of the hexagon instead of its walls, and those edges round off first. That is why this form is not simply a standard cap screw with the top machined away.
The second consequence is the floor under the socket. As the socket gets shallower, the material between its floor and the bearing face gets thicker, which is helpful, but the wall between the hexagon corners and the outside of the head gets thinner, and that wall is what splits when a joint is over-tightened. The two effects pull against each other, and the drawing has to state both so that the head is not optimised by eye.
The third consequence is torque capacity, and it is the one that catches assembly lines. A screw of the same thread takes less torque than a full cap head, but it looks the same at a glance and uses the same key size. An operator, a torque table or a driver setting carried over from the standard part will over-torque the low head, and the failure appears at the socket rather than at the thread.
Stainless magnifies all three. It is softer than the hardened key that drives it, so a socket that is loaded at the corners wears visibly over a few assembly cycles, and the hexagon that accepted the key on the first build refuses it on the third.
The recorded range is M1 to M14, with lengths made to the drawing. Custom lengths up to 2,000 mm are subject to DFM review after drawing submission. For a low profile socket head cap screw the quotation carries head diameter and height, socket size and depth, the floor thickness under the socket, thread and overall length.
| Item | How it is defined | What we control |
|---|---|---|
| Head | PF, low cylindrical head | Diameter, height and top edge |
| Socket | Hexagon in the low head | Across flats, depth and corner condition |
| Floor | Material under the socket | Thickness between floor and bearing face |
| Thread | Metric machine thread | Pitch, length and start position |
| Length | Overall, head included | Length tolerance and thread start |
| Material | A2 stainless | Grade and heat number on the certificate |
| Finish | Passivated, plain | Surface condition and socket edges |
Head height and socket depth should be quoted together, and the key that will be used should be named. A low head screw that is designed around a short key works; the same screw driven with a long key bottoms out in the socket and loads the wrong surfaces.
Head diameter stays at the standard value for the thread. Reducing both height and diameter produces a part that looks like a low head but has lost its bearing area, and the joint then marks the panel instead of clamping it.
Four features define these screws, and each is a trade against capacity:
| Feature | What it gives | What it costs |
|---|---|---|
| Reduced head height | Fits a shallow axial space | Shallower socket; less torque |
| Full head diameter | Bearing area unchanged | Head still needs radial clearance |
| Hexagon socket | Drive inside the head | Corner wear if over-torqued |
| Machine thread | Repeatable preload in a tapped hole | Needs a thread in the part behind |
| Plain stainless | Socket as formed; no coating | Softer than the key; galls in aluminium |
The value of the form is entirely axial. Where a cover sits a fraction above a frame, a standard cap head either fouls the cover or forces the design to raise the cover; a low head solves that without changing the thread or the drive size.
The cost is paid at the socket. A joint that needs high preload should not use a low head, no matter how convenient the space; for those joints the answer is a recess or a counterbore, not a shorter head.
The recorded finish is passivation on A2 stainless with no coating. On a low head screw that is the right choice for the same reason it matters on any socket screw: a coating would narrow the hexagon, and on a shallow socket a few micrometres of build is enough to change how the key seats.
| Option | How it protects | Effect on the low socket | Typical use |
|---|---|---|---|
| A2 stainless, passivated | Passive chromium oxide film | Socket as formed | Covers and instruments |
| A4 stainless, passivated | Passive film with molybdenum | Socket as formed | Marine and medical |
| Alloy steel, black oxide | Conversion film, oiled | No build; higher strength available | High-preload joints |
| Steel, zinc plated | Sacrificial zinc | Build in socket; re-checked | General indoor machinery |
| Stainless, silver plated | Passive film plus soft layer | Thin build; reduces galling | Repeated assembly |
Where a joint is opened often, socket wear is the limiting life, and a silver-plated stainless screw lasts noticeably longer than a plain one in an aluminium thread, because the plating takes the friction that would otherwise work-hardens the hexagon.
Where a coated steel screw is used for strength, the socket is gauged after plating. A shallow hexagon is far less tolerant of build than a full-depth one, and a screw that measures correctly can still refuse the production key.
Three assemblies where head height, not thread size, is the constraint:
| Where it sits | The screw holds a cover that sits a few tenths above the frame, so a standard cap head would foul it. |
| When it goes wrong | A standard head is substituted on the line and the cover no longer seats. |
| Why it happens | The axial space is tight, the thread is standard, and the drive is a key. |
| What we control | Head height and socket depth checked; first article fitted under the cover. |
| Where it sits | The screw fixes a board or a bracket where the head has to clear components on the board. |
| When it goes wrong | The head touches a component and the board flexes when the screw is tightened. |
| Why it happens | The clearance is small, the joint is inside an enclosure, and the drive is internal. |
| What we control | Head height checked against the clearance; first article fitted in the enclosure. |
| Where it sits | The screw closes a housing whose wall is too thin to recess a full cap head. |
| When it goes wrong | The wall is countersunk to fit the head and then cracks at the thread. |
| Why it happens | The wall is thin, the head must stay low, and the thread is in the housing. |
| What we control | Head and thread checked; first article assembled and reopened. |
Four reasons that matter on a screw whose capacity is set by a short head, each tied to something the drawing has to prove:
|
Head height and socket agreed
Head height, socket depth and the key that will be used are agreed as a set, because the drive capacity of a low head is decided by those three. Basis: Head height and socket agreed. |
Formed, socketed and passivated in one route
The low head and the socket are formed in one stroke, the thread rolled and the parts passivated as a batch. Basis: One route from wire to passivated screw. |
|
Socket gauged with the production key
The socket is proved with the production key at the joint torque, because a shallow hexagon can pass measurement and fail the first turn. Basis: Socket proved with the key. |
First article fitted under the cover
The first article is fitted in the assembly it belongs to, because the point of a low head is clearance that only the part can prove. Basis: First article fitted in the assembly. |
These screws are headed on single-die machines that form the low cylindrical head and cut the hexagon socket in one stroke, then rolled with the machine thread and passivated as a batch. The first part of every run is measured on head diameter and height, socket depth, floor thickness and thread.
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Cutting a hexagon into a short head is the constraint that defines the process. The punch has to reach a depth that gives the key enough engagement while leaving a wall thick enough to take the torque, and both of those are measured from a head that is not tall. A punch that is slightly deep produces a screw that measures correctly and splits at the corners on the first hard turn.
The head is formed before the socket, and its height is set by the die. When the die wears, the head grows slowly and the socket depth changes with it, so a batch-to-batch comparison accepts the drift; the check is made on the first part of every run against the drawing rather than against the previous batch.
What decides whether these parts pass is the head height, the socket, the floor under the socket and the thread. The inspection agreement covers those, and the criteria come from the drawing.
Head height and socket |
Thread and start checked |
Core hardness checked |
Salt-spray testing of the grade |
Head height and diameter are measured on a projector, and the socket is checked with the production key and then driven at the agreed torque under a controlled driver. The floor under the socket is measured from a sectioned sample at the start of a run, because it is the dimension that decides whether the head survives and it cannot be seen from outside.
A sample from every batch is driven into the customer’s assembly and then removed. On these parts the check that matters is removal: a socket that takes the driving torque and rounds on the way out has failed, and on a part inside a closed cover there is no second chance to get it out.
Every batch is traceable to the wire it was made from and to the passivation batch 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 and, where the grade is listed, the third-party report that covers it. The documents carry the drawing revision and the batch number, so a repeat order keeps the same head height and the same socket.
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 low head screw the first article is fitted under the cover it is meant to clear, because that clearance is the reason the part exists. 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 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 |
Head height. The diameter and the thread stay standard, so the bearing area is the same but the socket is shallower.
No. A low head takes less torque than a full cap head of the same size, and the socket fails first if the setting is carried over.
The size the socket was formed for, in a length that does not bottom out. A long key loads the wrong surfaces in a shallow socket.
Stainless is softer than the key. Repeated assembly at the wrong torque rounds the corners, and the hexagon then refuses the key.
When the joint needs high preload. Use a counterbore and a standard cap head instead of shortening the head.
Head diameter and height, socket size and depth, thread pitch, overall length and the intended driving key.
How a low profile socket head cap screw project runs from drawing to repeat delivery:
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1
Send the drawing and the clearance
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→ |
2
Head height and socket agreed
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→ |
3
First article fitted under the cover
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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 height, socket size and depth, thread pitch, overall length and the key you will use.
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Head diameter
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Head height
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Socket size
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Socket depth
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Thread pitch
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Overall 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
