The DIN912 hex socket head cap screw, commonly known as an Allen bolt or socket cap screw, is a cylindrical-head fastener driven by a hexagonal (Allen) key inserted into the recess on top of the head. It is manufactured according to the German DIN 912 standard, which specifies precise dimensional tolerances for thread pitch, head diameter, socket depth, and overall length. This standard is widely recognized and cross-referenced with ISO 4762 and ASME B18.3, making DIN912 screws globally interchangeable in most industrial assemblies.
The defining characteristic of this fastener is its compact, high-profile cylindrical head combined with an internal hex drive. Unlike external hex bolts that require a wrench swung around the fastener, DIN912 screws can be driven in confined spaces using only a straight Allen key or hex bit. This makes them the preferred choice in precision engineering, robotics, and modular mechanical assemblies where workspace is limited.
As a hardware and fasteners category product, the DIN912 is one of the most versatile and widely stocked fasteners in Tuyue's full product lineup.
Understanding the dimensional standard is essential for correct sourcing and engineering fit. The DIN912 standard defines the following key parameters:
Thread sizes range from M1.6 through M64, covering micro-assembly applications up to heavy structural bolting. The most common industrial sizes are M3 through M20. Thread pitch follows the ISO metric coarse series by default, though fine-pitch variants exist for specific engineering requirements.
Head diameter (dk) is nominally 1.5 times the nominal thread diameter. For example, an M8 screw has a head diameter of approximately 13 mm. Head height (k) is nominally equal to the thread diameter — an M8 head is 8 mm tall. Socket size (s) follows the standard Allen key series: M8 uses a 6 mm hex key, M10 uses 8 mm, and M12 uses 10 mm.
Minimum socket depth is critical to torque transfer and varies by size. An insufficient socket depth causes Allen key cam-out, stripping the socket. All DIN912 fasteners supplied through Tuyue are manufactured to full socket-depth specification to prevent this failure mode.
Thread tolerance follows the 6g standard for external threads, which provides a small clearance fit suitable for standard tapped holes produced to 6H tolerance. For assemblies requiring closer fits — such as aerospace or hydraulic systems — threads manufactured to 4g/4H tolerance are available on request.
Length is measured from under the head to the tip of the thread, consistent with ISO convention for socket head cap screws.
Material selection is the most critical engineering decision when specifying DIN912 screws. Different materials produce dramatically different mechanical performance and corrosion behavior.
Grade 12.9 Alloy Steel is the highest-strength commercially available DIN912 grade. With a minimum tensile strength of 1220 MPa and yield strength of 1100 MPa, it is the standard choice for high-load structural joints, clamping fixtures, and powertrain components. Grade 12.9 screws are typically surface-treated with black oxide or zinc phosphate, which provides mild corrosion resistance but is primarily a post-process that improves oil retention and reduces galling. Grade 12.9 is not suitable for strongly corrosive or salt-spray environments without additional coating.
Grade 10.9 Alloy Steel offers a tensile strength of 1040 MPa and is the workhorse grade for general industrial machinery. Most automotive assembly, construction equipment, and agricultural machinery applications specify 10.9 where corrosion is not a primary concern.
Grade 8.8 Carbon Steel is the entry-level structural grade with 800 MPa tensile strength. Suitable for light structural applications, furniture hardware, and general mechanical assembly.
Stainless Steel A2-70 (304 SS) provides excellent corrosion resistance in atmospheric, freshwater, and mild chemical environments. With a tensile strength of 700 MPa (A2-70 grade), it is suitable for food processing equipment, architectural installations, indoor electronics enclosures, and general outdoor applications. A2 stainless is not suitable for chloride-rich environments such as coastal or marine settings.
Stainless Steel A4-80 (316 SS) adds molybdenum to the alloy, providing resistance to chloride-induced pitting corrosion. With 800 MPa tensile strength, A4-80 is the material of choice for marine hardware, offshore equipment, chemical processing, and coastal construction. Tuyue's stainless steel bolt nut screws washers range includes both A2 and A4 grades for full project compatibility.
Titanium Grade 5 (Ti-6Al-4V) is available as a specialty option for aerospace, medical device, and high-performance motorsport applications where minimum weight combined with high strength is required. Density is approximately 60% that of steel while tensile strength exceeds 900 MPa.
Surface treatment affects both corrosion resistance and torque-tension behavior, making it an engineering parameter rather than a cosmetic choice.
Black Oxide (Blackening) is a chemical conversion coating that provides minimal corrosion protection (typically 24–48 hours salt spray) but significantly improves oil retention and gives a clean, low-reflectance appearance. Standard for Grade 12.9 screws. Always used with assembly oil or grease to achieve the intended corrosion protection level.
Zinc Electroplating (clear or yellow chromate) provides moderate corrosion resistance (72–120 hours salt spray per ISO 9227) and is common on Grade 8.8 and 10.9 carbon steel screws. Yellow chromate (hexavalent chrome) offers better corrosion resistance than clear but is restricted in EU markets under RoHS / ELV directives. Tuyue supplies trivalent chromate (Cr3+) finishes by default for EU-destined products to ensure compliance.
Hot-Dip Galvanizing provides a thick zinc layer (typically 45–85 µm) for outdoor structural applications. Note that hot-dip galvanizing affects thread dimensional tolerance; oversized nuts or re-tapping of threaded holes is required for reliable assembly.
Dacromet / Geomet coatings are thin-film inorganic zinc coatings that provide 480–1000 hours salt spray resistance with no hydrogen embrittlement risk — an important consideration for high-strength Grade 12.9 fasteners where electroplating can introduce hydrogen that causes delayed fracture.
Passivation for stainless steel restores the natural chromium oxide protective layer after machining or thread rolling, maximizing corrosion resistance for A2 and A4 grades.
The internal hex (Allen) drive of DIN912 screws enables precise torque application through a full-engagement hex key. Compared to Phillips or slotted drives, the hex socket allows significantly higher torque without cam-out, which is why DIN912 is preferred wherever specific preload (bolt tension) is required.
Recommended tightening torques (dry, unlubricated, for Grade 12.9) are approximately: M6 — 12 Nm; M8 — 29 Nm; M10 — 58 Nm; M12 — 100 Nm; M16 — 248 Nm. These values assume a friction coefficient of approximately 0.12–0.14. Lubricated joints require a torque reduction of approximately 25–30% to achieve the same preload, as lubrication reduces the friction component of tightening torque.
Hex key quality matters. Cheap Allen keys made from low-grade steel will round the socket before reaching the screw's full torque capacity. Industrial-grade S2 or Cr-V steel keys are recommended for repeated high-torque assembly.
For assemblies where vibration loosening is a concern, combining DIN912 screws with the appropriate hex socket round head machine screw variants and flat/split lock washers provides an integrated anti-vibration fastening system. Lock washers distribute load across the bearing surface and create mechanical resistance to rotational loosening.
Machinery & Industrial Equipment: DIN912 screws secure bearing housings, gearbox covers, motor mounting flanges, and structural frames. Grade 10.9 or 12.9 is standard in these applications. The recessed head is particularly valuable where a flush or sub-flush surface finish is needed on covers and guards.
Automotive & Motorsport: Engine block accessories, suspension components, brake caliper mounting, and interior trim panels use DIN912 in various materials depending on the environment. Titanium DIN912 screws are widely used in motorsport for weight reduction.
Electronics & Instrumentation: Small-diameter DIN912 screws (M2–M4) in A2 stainless or black oxide steel secure PCB standoffs, enclosure covers, and rack-mounted equipment. The compact head profile allows dense component placement.
Robotics & Automation: Joint actuators, servo motor mounts, linear rail systems, and end-effector tooling rely heavily on M4–M10 DIN912 in Grade 12.9 for maximum strength in minimum envelope. The precise torque delivery of hex socket drive is essential for joint preload consistency.
Solar & Photovoltaic Structures: A4 stainless DIN912 screws are used in rooftop and ground-mount PV racking systems. Tuyue's solar and photovoltaic module fastener solutions include compatible hardware designed to meet the specific corrosion and structural requirements of solar installations.
Furniture & Architectural Hardware: Furniture manufacturers use DIN912 for modular joinery because the flush head aesthetic is superior to hexagon bolt heads. Medium carbon steel with black oxide is the typical specification.
Construction & Structural Steelwork: For applications involving structural steel connections, DIN912 is often paired with flat washers to spread bearing load on softer substrate materials. For roofing and cladding systems, see Tuyue's roofing screws and drilling screws product range.
DIN912 (ISO 4762) — Full thread or partial thread socket cap screw with cylindrical head. The most common socket head standard globally.
ISO 7380 — Button head socket cap screw. Lower profile, wider bearing surface, lower torque capacity. Used where appearance and load distribution are more important than maximum clamping force. Tuyue supplies the hex socket round head bolt as a button-head variant suitable for applications requiring a lower-profile, wider-bearing-surface fastener.
DIN 7984 — Low head socket cap screw. Reduced head height compared to DIN912, used in thin sections where standard head height would create interference. Torque capacity is lower due to reduced socket depth.
DIN 6912 — Low head socket cap screw with pilot hole through the head, allowing through-head locking wire installation for safety-critical applications in aerospace and defense.
ISO 10642 (DIN 7991) — Countersunk (flat head) socket cap screw. Flush installation in countersunk holes. Tuyue's DIN965 cross flat head machine screw and DIN963 slotted flat head machine screw serve complementary flat-head applications across the fastener range.
Proper thread engagement is the foundation of reliable joint performance. The minimum recommended thread engagement length for steel-into-steel joints is 1.0× the nominal bolt diameter; for steel-into-aluminum, engagement should be 1.5–2.0× the diameter due to aluminum's lower bearing strength. Tapped blind holes should be deep enough to provide full thread engagement with clearance at the bottom to prevent bottom-out.
When designing tapped holes for DIN912 screws, use drill sizes and tap sizes per ISO 2306 metric coarse series. For M8 coarse thread, the tapping drill is 6.8 mm diameter. For fine-pitch M8 × 1.0, the tapping drill is 7.0 mm. Incorrect tapping drill selection is a leading cause of stripped threads in production.
Preload — the tension placed in the bolt during tightening — determines joint clamping force and resistance to loosening. For critical joints, torque-tension calibration should be performed using the actual bolt, nut, and surface finish combination, as friction variability can cause preload scatter of ±25–30% even with controlled torque. Torque-to-yield (TTY) or direct tension indicating (DTI) methods reduce this scatter for safety-critical applications.
Tuyue supplies DIN912 hex socket head cap screws in bulk packaging (carton or bag), reel, or custom retail packaging for distribution customers. Standard stock sizes span M3 through M20 in lengths from 6 mm to 200 mm, covering the vast majority of industrial application needs.
Custom sizes — including non-standard lengths, extra-fine pitch threads, custom head markings, or proprietary surface treatments — are available with agreed minimum order quantities. Tuyue's engineering team can provide DXF/PDF technical drawings and material certifications (mill certs, 3.1 inspection certificates per EN 10204) on request.
For complete project quoting including washers, nuts, and complementary fasteners, explore the full fasteners screws category or the broader stainless steel bolt nut screws washers collection for coordinated hardware procurement.
For special-purpose fasteners beyond standard categories, Tuyue's specialty and others range covers custom and low-volume requirements.
All fasteners manufactured and supplied by Zhejiang Jiaxing Tuyue Import And Export Co., Ltd. are subject to incoming material inspection, in-process dimensional checking, and finished-product verification including hardness testing, salt spray testing, and thread gauge inspection. Mechanical property testing is performed per ISO 898-1 for carbon and alloy steel fasteners and ISO 3506 for stainless steel grades.
Tuyue holds relevant trade and quality certifications that are verifiable through the company's official certifications page. Documentation packages for customs clearance, material compliance, and customer quality systems can be provided upon request.
For any technical or commercial questions, visit the FAQ page or reach the Tuyue export team directly via email at office@zjraise.cn / export@zjraise.cn or by phone at +86-573-82646333. The company is headquartered at RM1402–1404 Mingzhu Square, Jiaxing, Zhejiang, China 314001.
Zhejiang Jiaxing Tuyue Import And Export Co., Ltd. is a one-stop fastener supplier with an established export track record serving customers across Europe, North America, the Middle East, and Southeast Asia. The company's dual product focus — hardware and fasteners alongside oilless self-lubricating bearings — means that buyers of mechanical components can consolidate multiple product categories into a single supply relationship, reducing logistics cost and supplier management complexity.
Competitive pricing, reliable lead times, responsive pre-sales technical support, and the ability to provide full documentation packages make Tuyue a practical sourcing partner for distributors, OEMs, and project buyers who require consistent quality at commercial-grade pricing. Contact Tuyue today to request a quotation or discuss custom fastener requirements.
