Our DIN7991 countersunk socket head cap bolts for steel construction, machinery and equipment. Our range covers M3–M24 in 8.8/10.9/12.9 alloy steel and A2/A4 stainless, with DIN7991/ISO10642 dimension control, strict socket size inspection, and tested strength grades. Whether you are building a steel frame that requires flush trim, mounting machinery guards or assembling aluminum extrusions in a light-steel job, we can deliver the right size and grade within standard lead time.
Why Choose Countersunk Socket Head Cap Bolt?
A countersunk socket head cap bolt (DIN7991 / ISO10642) is the cleanest way to fix a cover, guard, panel or trim flush against its surface. Its 90° flat head seats level with the work face, the internal hexagon socket drives from directly above, and the finished join stays flat, snag-free and visually neat. Here is why a countersunk socket screw earns its place over a hex or button head wherever flatness, safety and appearance matter:
Flush, Snag-Free Surface
The flat 90° head disappears level with the surface, so covers, guards, panels and sliding surfaces stay continuous - nothing protrudes to catch clothing, tools, cables or moving parts.
Hex Socket Drive - Top Mounting & Anti-Strip
An Allen key engages from directly above, ideal for recessed or tight joints where a wrench cannot reach. Precise socket size and chamfer reduce key rounding on the drive.
Engineered Head Geometry That Seats True
Head diameter, height and 90° angle are held to DIN7991 / ISO10642, so the screw sits flush and perpendicular in the countersunk hole rather than rocking.
Strength Options for Every Load
8.8 for general use, 10.9/12.9 alloy for higher torque and small-size strength, and stainless A2/A4 where corrosion or hygiene matters - all tested per ISO 898-1 / ISO 3506.
Clean, Tamper-Concealed Assembly
For enclosure doors, access panels and trim, a flush screw hides the fix point - cleaner lines and less to catch or damage on the finished product.
Environment-Matched Finishes
Zinc for indoor, Dacromet / HDG or stainless A4 for outdoor and maritime, black oxide for tooling - coated or passivated as your use demands.
Head Geometry & Socket Drive
Two details decide whether a countersunk bolt seats perfectly or wobbles: the countersink angle and the socket drive size.
| Item | Standard / Detail |
|---|---|
| Countersink Angle | 90° flat (M3–M20) · 60° (M24) per DIN7991 |
| Head Diameter dk | e.g. M6→12 · M8→16 · M10→20 mm |
| Head Height k | e.g. M6→3.3 · M8→4.4 · M10→5.5 mm |
| Socket Size s | e.g. M6→4.02 · M8→5.02 · M10→6.02 mm |
| Anti-Strip Tip | Precise chamfer & gauge-checked socket reduce Allen key slipping (rounding) |
Buyer tip: always match the countersunk hole to the head. A 90° head needs a 90° hole; if your hole is 60° or your surface is thin, tell us and we recommend the right head or a flat-head alternative.
Standard Cross-Reference
| Standard | Region / Usage | |
|---|---|---|
| DIN7991 | DIN7991 | De facto metric (Germany / EU) - widely ordered size series |
| ISO10642 | ISO10642 | ISO replacement, tighter & interchangeable with DIN7991 in most sizes |
| GB/T70.3 | GB/T70.3 | Chinese national standard (equal to ISO10642) |
| ANSI/ASME B18.3 | ANSI/ASME B18.3 | Inch / unified series for the US market |
Comprehensive Product Specification
| Product | Countersunk Socket Head Cap Bolt (CSK Flat Head Screw) |
| Standard | DIN7991 · ISO10642 · GB/T70.3 · ANSI/ASME B18.3 |
| Head Angle | 90° (M3–M20) · 60° (M24) |
| Material | Alloy steel (e.g. SCM435, 40Cr) · Carbon steel · Stainless 304/A2, 316/A4 |
| Strength Class | 8.8 · 10.9 · 12.9 (ISO898-1); Stainless A2-70, A4-70/80 (ISO3506) |
| Size Range | M3 – M24 (common M3–M16) |
| Thread | ISO metric coarse, tolerance 6g; full or partial thread per spec |
| Length | 6 – 200 mm; length includes the head (metric countersunk) |
| Finish | Zinc plated (blue/white/yellow) · Black oxide · Dacromet · Cadmium substitute · Plain/Passivated |
| Uses | Machine covers & guards · jigs, molds & fixtures · aluminum extrusions · electronics & enclosures · sliding guides · furniture & door hardware · steel panels |
| MOQ / Sample | Flexible low MOQ · free samples in 3–5 working days |
| Packing & Delivery | Box → carton ≤25kg → pallet or wooden case; stock 7–10 days, OEM 10–15 days |
| Certificates | ISO 9001 · MTC / COA · hardness & salt-spray reports · third-party on request |
Dimension Chart (M3 – M16, 90° Head)
| d | Pitch | dk max | k max | Socket s |
|---|---|---|---|---|
| M3 | 0.5 | 5.7 | 1.7 | 2.0 |
| M4 | 0.7 | 7.64 | 2.3 | 2.5 |
| M5 | 0.8 | 9.64 | 2.8 | 3.0 |
| M6 | 1.0 | 11.57 | 3.3 | 4.0 |
| M8 | 1.25 | 15.57 | 4.4 | 5.0 |
| M10 | 1.5 | 19.48 | 5.5 | 6.0 |
| M12 | 1.75 | 23.48 | 6.5 | 8.0 |
| M16 | 2.0 | 31 | 9 | 10 |
Note:Dimension values are typical maxima/reference for guidance - confirm the drawing-matched table before ordering. M24 (60° head) available on request.
Applications of Countersunk Socket Head Cap Bolt
In steel construction, countersunk socket head cap bolts are used where a flat, safe surface is required on secondary parts and trim.
| Steel Structure Member / Location | How the CSK Bolt Is Used |
|---|---|
| Steel platform & mezzanine floor plates | Flush-fixing floor plates & checker-plate over the frame, leaving a flat trip-free walking surface |
| Steel stair treads & nosing | Countersunk head to secure steel treads, knock-grip plates and nosing flush to the stringer edge |
| Steel handrail posts & guardrail end plates | Flush-mounting handrail base plates & cap/trim plates so nothing snags the hand along the railing |
| Color-steel roof & wall sheeting on purlins | Fixing corrugated panels inside laps & edge trim flush to the purlin (Z/C section) - low head, no pull-over |
| Steel gusset & cover / trim plates | Holding cover plates and architectural trim flush over bolted nodes and gussets in steel frames |
| Steel frames & cabinets for equipment | Mounting guards, doors and access panels flush on steel equipment frames & enclosures |
| Light steel framing & partitions | Fixing mounting brackets, channels and thin plates onto light-gauge steel sections without a high head |
| Prefab / container-house trim & paneling | Flush assembly of wall panels, eaves trim and internal fit-out on modular steel units |
| Steel signboard & railing infill panels | Securing infill panels and signage flush so surfaces stay clean and safe to touch |
Note:These are secondary / non-load-bearing flush connections. For primary structural joints, choose high-strength hex bolts (DIN931/933) or TS twist-off bolts in Grade 8.8/10.9.
Our Quality Control
| Check | Detail |
|---|---|
| Head & Socket | Head diameter / height and socket size measured by gauge; anti-strip chamfer check |
| Thread | Go/No-Go on thread; pitch & profile per 6g |
| Strength | Tensile & hardness per ISO898-1; test-certified with MTC |
| Corrosion | Coating thickness & salt-spray test for plated / Dacromet parts |
| Traceability | Lot & heat marked; COA issued per batch |
Installation & Socket Torque Guide
1. Match the socket size
Use the correct Allen key (e.g. M6→4mm, M8→5mm, M10→6mm) for a full, non- slipping drive.
2. How length is measured
For a metric countersunk screw the nominal length includes the head. Thread starts below the head, so effective grip = nominal length minus head height.
3. Drive torque / strip prevention
Apply the recommended torque for the grade; over-driving a thin countersunk head can round the socket - when in doubt, use 12.9 alloy for small sizes.
Packaging, Lead Time & Shipping
Export-grade packing, clear lead time and flexible shipping for your countersunk socket head cap bolt order - with full shipping documents on request.
| Item | Details |
|---|---|
| Internal Packing | PE bags or boxes by size & lot; plain bulk or client-labeled |
| Outer Packing | Carton ≤25 kg → pallet with stretch film & corner guards; wooden cases for export |
| Samples | Free samples dispatched within 3–5 working days |
| Lead Time · Stock | Common sizes in stock: 7–10 days; standard custom production: 10–15 days; large/custom lots per schedule |
| Documents | Commercial Invoice, Packing List, MTC / COA, Certificate of Origin / Form A |
Note:Lead time and transit are indicative for standard lines; confirm exact schedule with your sales contact.
FAQ:
Is DIN7991 the same as ISO10642?
ISO10642 replaces DIN 7991 for metric countersunk socket screws; most sizes are interchangeable. We supply to either standard as you specify.
Why is my Allen key slipping on the screw?
Usually a worn socket, wrong key size, or over-torque. Use the exact matching key (see table) and, for small diameters, 12.9 alloy resists socket rounding.
Are these suitable for structural steel?
No - countersunk conical heads are for flush/aesthetic and moderate-load use. For structural connections we offer DIN931/933 hex bolts and TS high-strength bolts.
Do you supply M24 with the 60° head?
Yes, M24 in the 60° flat head per DIN7991 dimension table is available on order.
