Button Head Flange Screws (Button Flange Socket Screws)
In compact assemblies, the head shape is not cosmetic—it controls clearance, clamp stability, and rework risk. A Button Head Flange Screw combines a low-profile button head with an integrated flange/collar under the head to spread bearing load without adding a washer stack. This is particularly useful on painted sheet metal, aluminium brackets, and polymer housings, where local crushing (embedment) quickly reduces preload and invites fretting under vibration.
The common failure mode is predictable: the screw is tightened to torque, but the joint “settles” as coatings creep and the surface yields; clamp load drops and the assembly starts to rattle. The flange version increases bearing area to reduce contact pressure and helps stabilise preload. For production lines aiming to reduce tool slip and improve drive life, Torx (star) drive options also mitigate cam-out compared with worn internal hex tools—especially on high-cycle service work.
- Integrate flange; replace washers
- Reduce embedment; retain preload
- Lower head; protect clearances
- Offer Torx; cut cam-out risk
- Support Class 10.9 / 12.9
- Provide A2-70 / A4-80
Technical Specifications
Product Name
Button Head Flange Screws / Button Head Flange Cap Screws
Standards
ISO 7380-2 (button head with collar/flange, hex socket baseline); Torx/star drive per customer drawing; inch equivalents available by custom
Material
Alloy steel (e.g., SCM435 / 42CrMo / 4140 Q&T), Carbon steel (program-dependent), Stainless steel A2 (304) / A4 (316)
Grades
Metric steel: 10.9 / 12.9 (per ISO 898-1); Stainless: A2-70 / A4-70 / A4-80 (per ISO 3506, when specified)
Diameter Range
Typical metric: M3–M16 (other sizes on request); length per drawing
Surface Finish
Zinc plated (Cr3), Zinc-Nickel, Black oxide, Geomet/Dacromet (flake coating), Phosphate & oil, Passivation (stainless)
Certifications
ISO 9001:2015, EN 10204 3.1 MTC, RoHS/REACH declarations on request; PPAP/traceability options for OEM programs
1: Clamp-loss from embedment (soft substrates, coatings).
What happens in practice: Painted sheet metal and aluminium brackets compress under the head after tightening. The torque value looks correct, but preload decays as the interface settles.
Why flange matters: Engineering logic: Pressure = Force / Area. The integrated flange increases bearing area, reducing contact pressure and slowing embedment—often improving long-term clamp retention without adding a washer.
2: Vibration-driven fretting at the bearing surface.
What happens in service: Once preload drops, micro-slip starts. This creates fretting debris, damages coatings, and accelerates loosening in brackets, enclosures, and light machinery.
Solution path: maintain preload (flange + controlled torque), and if validation requires, combine with a locking strategy (threadlocker, prevailing torque nut, or wedge-lock washer—selected by test, not habit).
3: Tool slip / drive damage during high-cycle assembly.
What happens on the line: Internal hex drives can round when tools are worn or engagement is partial, leading to rework delays.
Torx advantage: Torx/star drive provides more engagement and reduces cam-out in automated or high-cycle tightening. For procurement, call out the drive type explicitly to avoid mixed inventory.
4: Galvanic corrosion and coating damage.
What happens outdoors: Under-head moisture traps and damaged finishes initiate corrosion. Stainless fasteners in aluminium assemblies can create galvanic couples depending on environment.
Engineering response: specify finish system (zinc-nickel or flake coatings) or use A4/316 for chloride exposure; manage lubrication to prevent stainless galling.
Example dimensions for “Button Head Flange Screw dimensions” searches. Confirm against your specified standard edition and drawing tolerances.
| Thread d | Pitch P (coarse) | Drive (example) | Head Ø dk (typ.) | Head height k (typ.) | Flange Ø dc (typ.) |
|---|---|---|---|---|---|
| M3 | 0.5 | Hex/Torx | 5.7 | 1.65 | 7.5 |
| M4 | 0.7 | Hex/Torx | 7.6 | 2.20 | 10.0 |
| M5 | 0.8 | Hex/Torx | 9.5 | 2.75 | 12.0 |
| M6 | 1.0 | Hex/Torx | 10.5 | 3.30 | 14.0 |
| M8 | 1.25 | Hex/Torx | 14.0 | 4.40 | 18.0 |
| M10 | 1.5 | Hex/Torx | 17.5 | 5.50 | 22.0 |
Why the flange diameter matters
dc drives bearing pressure, coating survival, and embedment rate.
If the joint face is soft or painted, dc is often more important than head height in predicting preload stability.
Achieve repeatable preload while protecting the mating surface and drive.
Hole Clearance (ISO 273)
For through-holes, use ISO 273 close/normal/large clearance series based on your assembly tolerance and alignment method.
Binding shanks create false torque and lower preload; oversized holes increase slip risk under transverse load.
Torque, Preload, Lubrication (process control)
Torque is friction-dominated. Define the assembly condition (dry vs oiled vs coated) and keep it consistent.
Practical relationship: T = K × F × d (K varies with finish/lube).
Indicative K ranges: dry 0.18–0.25, light oil 0.14–0.20, anti-seize 0.10–0.16.
For critical joints, validate torque–tension behaviour (e.g., ISO 16047 style testing) and specify acceptable friction window.
Washer strategy
The flange is designed to reduce reliance on washers; however washers may still be needed when:
slot holes exist
electrical isolation is required
the surface is extremely soft and needs a larger OD than the flange provides
Drive protection (avoid stripping)
Ensure full driver engagement depth; avoid ball-end keys for final torque.
For Torx, match the correct bit size and replace worn bits early—most drive failures start with tool wear, not screw hardness.
Corrosion + galvanic control
For outdoor assemblies: specify coating system and avoid damaging topcoats during tightening.
For stainless in aluminium: consider barrier coatings, isolating washers, or validated anti-seize to reduce galling and galvanic risk.
Related Products
FAQ
What is a button head flange screw?
A button head flange screw is a low-profile screw with an integrated flange (collar) under the head to spread load and reduce embedment. It is used to improve clamp stability without adding a separate washer.
Which standard covers button head screws with a collar?
ISO 7380-2 covers button head screws with an integral collar (flange). ISO 7380-1 is the non-collar version, so procurement should specify “-2” when flange is required.
Why use a flange screw instead of a washer?
A flange screw reduces parts count and provides a controlled under-head bearing surface, which can improve repeatability on assembly lines. It also reduces the risk of missing washers and helps stabilise preload on coated or softer surfaces.
Torx vs hex socket—what should I choose?
Torx generally reduces cam-out risk and can improve tool life in high-cycle tightening, while hex socket is widely compatible and common for service. The right choice depends on torque level, rework frequency, and tool control on the production line.
Can you supply button head flange screws in stainless steel?
Yes—common stainless options include A2-70 (304) and A4-70/A4-80 (316). Stainless is selected for corrosion resistance, but the assembly process should control galling risk through lubrication and compatible mating components.