Socket
Button Head
Cap Screws
Low-profile domed Allen drive fastener in Grade 10.9, 12.9 high tensile and SS 304 / 316. Manufactured to ISO 7380-1. Metric M3–M12 in ready stock from Bengaluru — the go-to fastener for machinery covers, automotive panels, and consumer electronics.
Grade
10.9 · 12.9 · SS 304 · SS 316
Standard
ISO 7380-1
Size Range
M3 – M12
What is a Socket Button Head Cap Screw?
A socket button head cap screw — commonly abbreviated BHCS — is a precision fastener with a low-profile, domed head driven by an internal hexagonal (Allen) socket. Unlike the tall cylindrical head of a standard socket head cap screw, the button head sits close to flush with the parent surface, eliminating sharp protrusions and giving a clean, snag-free finish. The wide dome also spreads the clamping load over a larger bearing area.
RM Traders stocks button head cap screws in Grade 10.9 and Grade 12.9 high tensile — with Black Oxide finish as standard and Zinc plating available on request — and in SS 304 stainless for corrosion-resistant applications. Metric sizes M3 to M12.
High Tensile
Grade 10.9
Min tensile strength 1040 MPa. General high-tensile machine and structural applications. Black Oxide standard; Zinc on request. Per ISO 898-1.
High Tensile
Grade 12.9
Min tensile strength 1220 MPa. Maximum strength grade. Black Oxide standard; Zinc on request with de-embrittlement bake per ISO 4042.
Corrosion Resistant
SS 304 / 316
Austenitic stainless. SS 304 in ready stock. SS 316 (molybdenum for chloride resistance) available on special order. No coating required.
Standards & Specifications
- ISO 7380-1International standard for socket button head cap screws — plain, no flange under the head. Specifies head diameter (dk), head height (k), socket size (s), socket depth, and thread tolerances for M3–M16. Product Grade A per ISO 4759-1. This is what RM Traders stocks.
- ISO 7380-2ISO 7380-2 covers the flange button head variant — identical domed head but with an integral wide flange (washer face) under the dome for a larger bearing area. Useful on soft materials or oversized clearance holes; visually distinguishable by the flat rim around the dome base. RM Traders stocks this variant — view the Flange Button Head page.
- ISO 898-1Mechanical properties for property classes 10.9 and 12.9. Minimum specified property class for ISO 7380-1 is 10.9 — the shallow domed head limits socket engagement depth and therefore maximum drive-out torque versus a standard socket head cap screw.
- ThreadISO metric coarse thread per ISO 261 / ISO 965-2. Thread tolerance class 6g. Fully threaded for all standard lengths in the M3–M12 range.
Dimensional
Tolerances
Per ISO 7380-1 — Product Grade A. All dimensions in mm.
| d | p (mm) | Head dia dk (mm) | Head height k (mm) | A/F — s (mm) | t min (mm) | ||||
|---|---|---|---|---|---|---|---|---|---|
| max | min | max | min | nom | max | min | |||
| M3 | 0.50 | 5.70 | 5.40 | 1.65 | 1.40 | 2 | 2.08 | 2.02 | 1.04 |
| M4 | 0.70 | 7.60 | 7.24 | 2.20 | 1.95 | 2.5 | 2.58 | 2.52 | 1.30 |
| M5 | 0.80 | 9.50 | 9.14 | 2.75 | 2.50 | 3 | 3.08 | 3.02 | 1.56 |
| M6 | 1.00 | 10.50 | 10.07 | 3.30 | 3.00 | 4 | 4.095 | 4.02 | 2.08 |
| M8 | 1.25 | 14.00 | 13.57 | 4.40 | 4.10 | 5 | 5.14 | 5.02 | 2.60 |
| M10 | 1.50 | 17.50 | 17.07 | 5.50 | 5.20 | 6 | 6.14 | 6.02 | 3.12 |
| M12 | 1.75 | 21.00 | 20.48 | 6.60 | 6.24 | 8 | 8.175 | 8.025 | 4.16 |
dk = head diameter · k = head height · s = across flat (A/F) hex socket size · t = minimum socket engagement depth · p = thread pitch. Note: button head screws use a smaller Allen key than same-diameter socket head cap screws — use the correct Allen key size.
Sizes Available
Standard stocked metric range in High tensile (Grade 10.9 & 12.9) and SS 304. Sizes outside these ranges available on enquiry with MOQ.
HT Grade 10.9 & 12.9 — Metric (M3 – M12)
| Diameter | Available Lengths (mm) |
|---|---|
| M3 | 6, 8, 10, 12, 16, 20, 25 |
| M4 | 6, 8, 10, 12, 16, 20, 25, 30, 35 |
| M5 | 6, 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 |
| M6 | 8, 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 |
| M8 | 10, 12, 16, 20, 25, 30, 35, 40, 45, 50 |
| M10 | 16, 20, 25, 30, 35, 40, 45, 50 |
| M12 | 20, 25, 30, 35, 40, 45, 50 |
SS 304 — Metric (M3 – M10)
| Diameter | Available Lengths (mm) |
|---|---|
| M3 | 6, 8, 10, 12, 16, 20, 25, 30 |
| M4 | 6, 8, 10, 12, 16, 20, 25, 30, 35, 40 |
| M5 | 6, 8, 10, 12, 16, 20, 25, 30, 35, 40 |
| M6 | 10, 12, 16, 20, 25, 30, 35, 40, 50, 60 |
| M8 | 16, 20, 25, 30, 35, 40, 50, 60 |
| M10 | 20, 25, 30, 35, 40, 50, 60 |
All HT sizes are fully threaded. Finish: Black Oxide standard for Grade 10.9 & 12.9; Zinc plating available on customer request.
SS 316 available only on customer order — same diameter range as SS 304 above; lead time 7–14 days. Contact us for MOQ and pricing.
SS 316 available only on customer order — same diameter range as SS 304 above; lead time 7–14 days. Contact us for MOQ and pricing.
Applications
Machinery Covers & Guards
Button heads are the standard fastener for access panels, safety guards and inspection covers on industrial machinery — the low profile prevents snagging on clothing, hoses and cables.
Automotive Panels
Used on interior trim panels, underbody covers and cosmetic brackets where a flush, clean appearance is required and the head must not protrude into passenger space or adjacent body panels.
Consumer Electronics
Enclosures, chassis and rack-mount equipment use Grade 10.9 button heads for their compact head, no-snag profile, and clean appearance in consumer-facing products.
Furniture & Fixtures
Office chairs, commercial shelving and display fixtures specify button heads where structural joints must be safe — no sharp edges — and visually acceptable without a cap or cover.
Robotics & Frames
Aluminium extrusion frames, servo covers and link assemblies in collaborative robots favour button heads for low-profile assembly within tight clearances between moving joints.
Marine & Food Equipment
SS 304 / SS 316 button heads are used on marine hardware, food-processing equipment covers and pharmaceutical panels where hygiene, corrosion resistance and snag-free surfaces are mandatory.
Frequently Asked
Questions
What is a socket button head cap screw?
A socket button head cap screw (BHCS) is a fastener with a low-profile, domed head driven by an internal hexagonal (Allen) socket. Manufactured to ISO 7380-1, the wide button-shaped head sits nearly flush with the parent surface — eliminating the sharp edges and protrusions of a standard hex bolt or socket head cap screw. This makes it the preferred fastener in machinery covers, automotive panels, consumer electronics, and furniture where safety, aesthetics, and low-clearance assembly are the primary requirements.
What is the difference between a button head and a socket head cap screw?
The key difference is head profile and maximum clamping strength. A socket head cap screw (DIN 912 / ISO 4762) has a tall cylindrical head with a deep socket — it can be tightened to very high torque and clamping force. A socket button head cap screw (ISO 7380-1) has a low, wide dome head at roughly 40–60% the height of a socket head. The shallower dome means a smaller socket with less engagement depth, so maximum torque capacity is lower. Use button heads where appearance, low clearance, or snag-safety matter most; use socket head cap screws where maximum clamping force is the priority. Do not substitute one for the other in high-load structural applications without engineering review.
What grade are socket button head cap screws available in?
RM Traders stocks button head cap screws in Grade 10.9 (minimum tensile strength 1040 MPa) and Grade 12.9 (1220 MPa) high tensile alloy steel, and in SS 304 stainless steel. ISO 7380-1 specifies a minimum property class of 10.9 for button head screws. Note that the domed geometry limits socket depth and therefore drive-out torque — for the highest load applications, socket head cap screws (DIN 912) are a better choice. SS 316 is available on customer order for chloride or marine environments.
Can socket button head cap screws be plated or coated?
Yes. For Grade 10.9 and 12.9 button heads, RM Traders supplies Black Oxide as standard and Zinc plating on customer request. Black Oxide gives a clean dark appearance with mild corrosion resistance — ideal for machinery and electronics. For Grade 12.9 Zinc-plated parts: electroplating generates hydrogen that can embrittle high-strength steel — a post-plating de-embrittlement bake at 200–230°C for ≥8 hours is mandatory per ISO 4042. Where this is a concern, specify Black Oxide or mechanical zinc (Dacromet / Geomet) — both are hydrogen-free. SS 304 and SS 316 stainless button heads require no coating.
What is ISO 7380-1, and what is the difference between ISO 7380-1 and ISO 7380-2?
ISO 7380 is the international standard family for socket button head cap screws, published in two parts. ISO 7380-1 covers the plain button head — a low-profile domed head with no flange, driven by an internal hex socket. It specifies head diameter (dk), head height (k), socket size (s), socket depth (t), thread form (ISO metric coarse, tolerance class 6g), and minimum property class 10.9. Sizes M3–M16. This is the standard RM Traders stocks.
ISO 7380-2 covers the flange button head — the same domed head but with an integral wide flat flange (washer face) under the dome. The flange increases the bearing area under the head, making it useful when fastening into soft materials (aluminium, plastic, wood) or when the clearance hole is slightly oversized. You can immediately tell the two apart: ISO 7380-2 has a visible flat rim around the base of the dome; ISO 7380-1 does not. RM Traders does not stock ISO 7380-2 — contact us if you need flange button heads.
ISO 7380-2 covers the flange button head — the same domed head but with an integral wide flat flange (washer face) under the dome. The flange increases the bearing area under the head, making it useful when fastening into soft materials (aluminium, plastic, wood) or when the clearance hole is slightly oversized. You can immediately tell the two apart: ISO 7380-2 has a visible flat rim around the base of the dome; ISO 7380-1 does not. RM Traders does not stock ISO 7380-2 — contact us if you need flange button heads.
What Allen key size fits each button head cap screw diameter?
Hex socket (Allen key) sizes per ISO 7380-1 for button head cap screws: M3 = 2 mm · M4 = 2.5 mm · M5 = 3 mm · M6 = 4 mm · M8 = 5 mm · M10 = 6 mm · M12 = 8 mm. Important: button head screws use a smaller Allen key than socket head cap screws of the same diameter — e.g. M6 button head uses 4 mm, M6 socket head uses 5 mm. The shallow dome limits socket depth, so always ensure the key is fully seated before torquing. Using the wrong (larger) Allen key or a worn key can round the socket, making removal very difficult.
Are socket button head cap screws available in stainless steel?
Yes. RM Traders stocks button head cap screws in SS 304 (A2) in metric M3 to M10, with lengths from 6 mm to 60 mm depending on diameter. SS 304 is suitable for indoor, mildly corrosive, and general outdoor environments. SS 316 (which adds molybdenum for superior chloride and marine resistance) is available on special order. Stainless button heads are rated A2-70 (700 MPa tensile) — excellent corrosion resistance but lower clamping strength than Grade 10.9 or 12.9 alloy steel.
Why are socket button head cap screws preferred in consumer electronics and furniture?
Button head cap screws are favoured in consumer electronics, furniture, and automotive panels for three reasons. Safety: the low domed profile has no sharp edges — it will not cut skin or snag fabric, cables, or adjacent components. Aesthetics: the smooth dome sits close to flush with the panel surface, giving a clean, minimal appearance. Low clearance: at roughly 40–60% the head height of a standard socket head cap screw, button heads fit in assemblies where panel thickness or adjacent component clearance would not allow a taller head — without the fully-recessed counterbore required for a countersunk screw.
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