Distribution Range · Vetted Partner Mills · Ahmedabad
CSK Allen Bolts Manufacturer & Precision Socket Fastener Distribution
Countersunk socket head screws (DIN 7991 / ISO 10642), socket head cap screws (DIN 912 / ISO 4762), and button head screws (DIN 7380) supplied across Property Classes 8.8, 10.9, 12.9, and austenitic stainless steel. Distributed from vetted partner mills in Ahmedabad with complete EN 10204 3.1 MTC pass-through and lot traceability.
Overview: socket fastener families & consolidated procurement model
In precision mechanical engineering and tool-room manufacturing, internal hexagon drive fasteners - colloquially referred to as Allen bolts - are specified wherever high clamp preload, compact head counterbores, or flush mounting geometry are demanded. Unlike standard external hexagon bolts that require perimeter spanner clearance, socket-head fasteners are tightened from within the head profile using a metric hex key or hex bit, enabling tighter joint center-to-center pitch and compact machinery envelopes.
The socket-head category on this page encompasses the three core head geometries that mechanical engineers and tool-room procurement managers routinely purchase in combination: countersunk socket head screws (DIN 7991 / ISO 10642) for flush-face assemblies, socket head cap screws (DIN 912 / ISO 4762) for high-torque mechanical clamp joints, and button head socket screws (DIN 7380 / ISO 7380-1) for clearance-constrained panels and sheet-metal housings. Low-head socket cap screws (DIN 7984) and socket set screws (DIN 913/914/916) are supplied on project order.
Transparency is fundamental to KP Fasteners’ engineering supply philosophy: we distribute precision socket-head fasteners through audit-verified primary mills. While our in-house manufacturing lines in our Ahmedabad manufacturing facility are dedicated to heavy custom in-house foundation bolts for heavy base frames, continuous threaded stud bolts, and sag rods, our wholesale distribution network allows machine builders, tool-rooms, and OEMs to consolidate their complete mechanical bill of materials (BOM).
Instead of managing separate supplier contracts for structural anchors and precision socket hardware, buyers consolidate orders under one purchase order, receiving matching hex nuts and washers alongside their socket bolts, accompanied by unified dispatch lot tagging and mill test certification.
Socket head families: geometry, drive mechanics & standards
Each socket head family serves a distinct mechanical boundary condition. Selecting the correct geometry ensures sufficient clamping force while adhering to surface clearance and counterbore machining limits.
Countersunk Socket Screws (CSK)
Engineered with a 90° flat conical head that seats fully inside a pre-countersunk pocket. Once torqued flush with the workpiece surface, the fastener creates zero clearance protrusion, preventing collision with sliding machine ways, conveyor rollers, or mated tooling plates.
- • Angle: 90° standard (ASME 82° on quote)
- • Drive: Metric internal hexagon
- • Typical Grades: 8.8, 10.9, SS A2-70
Socket Head Cap Screws (SHCS)
The industrial workhorse of machine assembly and tool-room manufacturing. Features a tall cylindrical head with deep internal hexagon socket walls that transmit high tightening torques without driver cam-out. Ideal for counterbored holes where perimeter clearance is restricted.
- • Profile: Full cylindrical head (head dia ≈ 1.5d)
- • Drive: Deep precision internal hexagon
- • Typical Grades: 10.9, 12.9, SS A4-70
Button Head Socket Screws
Designed with a wide-diameter, low-profile rounded dome head. The broad bearing surface distributes clamping force across thin sheet-metal skins or soft materials, while the smooth contour eliminates catch hazards on exposed machinery guards, automotive cabs, and electronics.
- • Profile: Low rounded dome with wide flange base
- • Drive: Low-profile internal hex socket
- • Typical Grades: 8.8, SS A2-70
Low-Head Socket Cap Screws
Employs a cylindrical head whose height is approximately 50% that of a standard DIN 912 cap screw. Specified where counterbore depth is strictly limited by remaining parent wall thickness, such as in compact hydraulic valve manifolds and thin-walled transmission housings.
- • Profile: Short cylindrical head for shallow bores
- • Drive: Compact internal hex socket
- • Typical Grades: 10.9, SS A2
Socket Set Screws (Grub Screws)
Fully threaded, headless fasteners containing an internal hex drive at one end and a specialized point at the other (cup point DIN 916, cone point DIN 914, flat point DIN 913). Used to lock pulleys, gears, timing sprockets, and bearing collars onto rotating drive shafts.
- • Profile: Headless continuous external thread
- • Points: Cup, cone, flat, dog point
- • Typical Grades: 45H, Grade 12.9, SS 304
Precision Ground Shoulder Bolts
Features a precision centerless-ground unthreaded cylindrical shoulder with strict diameter tolerances (h8/f9). Functions as a stationary pivot pin, linkage trunnion, or linear stripper guide shaft in stamping punch assemblies and spring-loaded mechanical mechanisms.
- • Profile: Ground precision shoulder + smaller thread
- • Drive: Hex socket in head
- • Typical Grades: 12.9 (core), ground finish
Engineering standards cross-reference & metric hex-key engagement
Cross-referencing DIN, ISO, and ASME standards ensures interchangeability on imported equipment. The hex-key engagement table below provides the exact wrench sizes required across nominal thread diameters.
Standards Harmonization: DIN vs. ISO vs. ASME
| Head Family | DIN Standard | ISO Standard | ASME Equivalent | Key Mechanical Characteristics |
|---|---|---|---|---|
| Countersunk socket (CSK) | DIN 7991 | ISO 10642 | ASME B18.3.5M | 90° flat conical head sits flush in pre-countersunk hole; unobstructed sliding contact |
| Socket head cap screw | DIN 912 | ISO 4762 | ASME B18.3 | Deep cylindrical head; accepts highest torque and preload; standard tool-room joint |
| Button head socket screw | DIN 7380 | ISO 7380-1 | - | Low rounded dome head; wide bearing area; prevents clothing/cable snagging |
| Low-head socket cap | DIN 7984 | ISO 14580 | - | Reduced cylindrical head height (~50% of DIN 912) for shallow counterbores |
| Socket set screw (cup/cone/flat) | DIN 913 / 914 / 916 | ISO 4026 / 4027 / 4029 | ASME B18.3 | Headless threaded grub screw with internal hex; fixes pulleys and gears to shafts |
| Precision shoulder bolt | DIN 923 / ISO 7379 | ISO 7379 | ASME B18.3 | Ground unthreaded shoulder acts as pivot pin or linear guide shaft for punch tooling |
Metric Hex-Key & Allen Drive Engagement Table
Internal hex dimensions dictate the size of the hex key (Allen wrench) or driver bit needed. Note that DIN 7380 button head screws employ a smaller internal socket than DIN 912 cap screws of the same thread diameter to preserve head crown wall thickness.
| Thread Size | Pitch (mm) | DIN 912 Socket Cap (Hex mm) | DIN 7991 CSK (Hex mm) | DIN 7380 Button Head (Hex mm) | Nominal Socket Depth (mm) |
|---|---|---|---|---|---|
| M3 | 0.50 | 2.5 mm | 2.0 mm | 2.0 mm | 1.5 mm |
| M4 | 0.70 | 3.0 mm | 2.5 mm | 2.5 mm | 2.0 mm |
| M5 | 0.80 | 4.0 mm | 3.0 mm | 3.0 mm | 2.5 mm |
| M6 | 1.00 | 5.0 mm | 4.0 mm | 4.0 mm | 3.0 mm |
| M8 | 1.25 | 6.0 mm | 5.0 mm | 5.0 mm | 4.0 mm |
| M10 | 1.50 | 8.0 mm | 6.0 mm | 6.0 mm | 5.0 mm |
| M12 | 1.75 | 10.0 mm | 8.0 mm | 8.0 mm | 6.0 mm |
| M14 | 2.00 | 12.0 mm | 10.0 mm | 10.0 mm | 7.0 mm |
| M16 | 2.00 | 14.0 mm | 10.0 mm | 10.0 mm | 8.0 mm |
| M20 | 2.50 | 17.0 mm | 14.0 mm | 14.0 mm | 10.0 mm |
| M24 | 3.00 | 19.0 mm | 17.0 mm | 17.0 mm | 12.0 mm |
Metric size schedule & dimensional specifications (M3 to M24)
Standard stocking inventory covers nominal thread diameters from M3 to M24 in lengths from 6 mm to 180 mm. Metric threads conform to ISO 965-2 coarse tolerance class 6g (bolts) and 6H (tapped holes).
| Nominal Thread | Pitch (mm) | Standard Length Range | Head Profiles Available | Applicable Standards | Routinely Stocked Grades |
|---|---|---|---|---|---|
| M3 | 0.50 | 6 - 30 mm | CSK, Cap, Button | DIN 7991, DIN 912, DIN 7380 | 8.8, SS A2 |
| M4 | 0.70 | 6 - 40 mm | CSK, Cap, Button | DIN 7991, DIN 912, DIN 7380 | 8.8, 10.9, 12.9, SS A2 |
| M5 | 0.80 | 8 - 50 mm | CSK, Cap, Button | DIN 7991, DIN 912, DIN 7380 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M6 | 1.00 | 10 - 70 mm | CSK, Cap, Button, Low-Head | DIN 7991, 912, 7380, 7984 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M8 | 1.25 | 12 - 90 mm | CSK, Cap, Button, Low-Head | DIN 7991, 912, 7380, 7984 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M10 | 1.50 | 16 - 100 mm | CSK, Cap, Button, Low-Head | DIN 7991, 912, 7380, 7984 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M12 | 1.75 | 20 - 120 mm | CSK, Cap, Button, Low-Head | DIN 7991, 912, 7380, 7984 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M14 | 2.00 | 25 - 130 mm | CSK, Cap | DIN 7991, DIN 912 | 10.9, 12.9 |
| M16 | 2.00 | 25 - 150 mm | CSK, Cap, Low-Head | DIN 7991, DIN 912, DIN 7984 | 8.8, 10.9, 12.9, SS A2, SS A4 |
| M20 | 2.50 | 35 - 160 mm | CSK, Cap | DIN 7991, DIN 912 | 10.9, 12.9, SS A4 |
| M24 | 3.00 | 45 - 180 mm | CSK, Cap | DIN 7991, DIN 912 | 10.9, 12.9 |
Threading Specification Note: In accordance with DIN 912 / ISO 4762, short socket head cap screws are threaded fully to the head, while longer lengths incorporate a partial unthreaded shank to resist heavy shear planes. Countersunk screws (DIN 7991) are generally fully threaded up to 50 mm length. Non-standard thread pitches (fine pitch M10×1.0, M12×1.25, M16×1.5) are available on confirmed quote.
Property classes, alloy metallurgy & surface finishes
The mechanical integrity of a bolted joint depends on matching property class to dynamic stress, preload, and environmental corrosivity. All socket fasteners are sourced with certified property-class head stampings.
Carbon & Alloy Steel Property Classes
- Property Class 8.8: Medium carbon steel, quenched and tempered. Nominal tensile strength of 800 MPa with minimum yield strength of 640 MPa. Used for general machine framing, bracket fixtures, and light structural covers.
- Property Class 10.9: Quenched and tempered boron or low-alloy steel. Nominal tensile strength of 1,040 MPa with minimum yield strength of 900 MPa. Recommended for high-stress machine elements, automotive suspension assemblies, and flange couplings.
- Property Class 12.9: High-grade alloy steel (typically 42CrMo4 / AISI 4140), precision heat-treated to a tensile strength of 1,220 MPa and yield strength of 1,080 MPa. The gold standard for stamping dies, injection moulds, and extreme fatigue environments.
Stainless Steel Grades (ISO 3506-1)
- Austenitic Stainless Steel A2-70 (AISI 304): Cold-worked austenitic stainless steel with minimum tensile strength of 700 MPa. Provides excellent resistance to atmospheric moisture, organic acids, and indoor industrial humidity. Ideal for cleanroom and food equipment.
- Austenitic Stainless Steel A4-70 / A4-80 (AISI 316): Molybdenum-alloyed austenitic stainless steel (2-3% Mo) providing outstanding pitting and crevice resistance in chloride-dense environments. Mandatory for coastal solar installations, marine deck hardware, and chemical reaction vessels.
Stocking Coverage: Head Family vs. Property Class
| Head Family | Property Class 8.8 | Property Class 10.9 | Property Class 12.9 | Stainless SS A2-70 | Stainless SS A4-70 / A4-80 |
|---|---|---|---|---|---|
| CSK (DIN 7991 / ISO 10642) | Stocked (Default) | Stocked | On-Quote | Stocked (A2-70) | Stocked (A4-70) |
| Socket Cap (DIN 912 / ISO 4762) | Stocked | Stocked (Default) | Stocked (Default Tooling) | Stocked (A2-70) | Stocked (A4-70 / A4-80) |
| Button Head (DIN 7380 / ISO 7380-1) | Stocked (Default) | On-Quote | Not Standard | Stocked (A2-70) | Stocked (A4-70) |
| Low-Head (DIN 7984 / ISO 14580) | On-Quote | Stocked | On-Quote | Stocked (A2-70) | On-Quote |
Socket fastener SKU configurations & variant matrix
Overview of standard catalog SKU combinations detailing head profile, international standard, material grade, coating system, and target engineering application.
| Product Family | Governing Standard | Material & Class | Protective Coating | Size Coverage | Primary Engineering Application |
|---|---|---|---|---|---|
| CSK Socket Screw | DIN 7991 / ISO 10642 | High-Tensile Steel (PC 10.9) | Black Oxide / Phosphated | M4 - M20 | Flush machine surfaces, guide plates, and punch tool retainers requiring high shear strength |
| CSK Socket Screw | DIN 7991 / ISO 10642 | Stainless Steel (A2-70 / 304) | Chemical Passivation (ASTM A967) | M3 - M16 | Food processing machinery, architectural trim, conveyor belts, and sanitary washdown housings |
| Socket Head Cap Screw | DIN 912 / ISO 4762 | Alloy Steel (PC 12.9) | Black Oxide (No HDG) | M5 - M24 | Injection moulding tool-rooms, stamping die blocks, hydraulic pump housings, and extreme shock loads |
| Socket Head Cap Screw | DIN 912 / ISO 4762 | Stainless Steel (A4-80 / 316) | Chemical Passivation (ASTM A967) | M6 - M20 | Coastal solar mounting rails, chemical reactors, offshore skids, and marine deck hardware |
| Button Head Socket Screw | DIN 7380 / ISO 7380-1 | Carbon Steel (PC 8.8) | Zinc Electroplated (IS 1573) | M4 - M12 | Sheet-metal machine guards, safety covers, automation conveyor frames, and light structural trim |
| Button Head Socket Screw | DIN 7380 / ISO 7380-1 | Stainless Steel (A2-70 / 304) | Natural Bright / Passivated | M3 - M10 | Electronics chassis, outdoor automation panels, instrumentation cabinets, and robotic end-effectors |
| Low-Head Socket Cap | DIN 7984 / ISO 14580 | Alloy Steel (PC 10.9) | Black Oxide | M6 - M16 | Shallow counterbores, compact hydraulic valve manifolds, and tight linear bearing blocks |
Engineering decision framework: selecting head geometry & grade
Use this application-driven selector to determine the ideal socket head profile, property class, and surface finish for your mechanical joint conditions.
| Application Context | Recommended Head Profile | Recommended Grade | Protective Coating | Engineering Rationale & Functional Advantage |
|---|---|---|---|---|
| Flush fit on an exposed sliding surface | CSK Socket (DIN 7991) | PC 8.8 / 10.9 / SS A2 | Black oxide / Zinc / Passivated | 90° countersunk pocket; zero head protrusion prevents collision with moving machine parts |
| High-torque machinery clamp joint | Socket Cap (DIN 912) | PC 10.9 / 12.9 | Black oxide | Full cylindrical head; accepts maximum tightening torque and clamp preload without stripping |
| Weight or clearance-sensitive cover | Button Head (DIN 7380) | PC 8.8 / SS A2 | Zinc / Passivated | Smooth dome contour distributes load across thin sheet metal; eliminates sharp catch hazards |
| Counterbore depth constrained by wall | Low-Head Cap (DIN 7984) | PC 10.9 | Black oxide | Head height is ~50% of DIN 912; preserves underlying metal thickness in compact housings |
| Plastic injection moulds & press dies | Socket Cap (DIN 912) | PC 12.9 | Black oxide (never HDG) | Yield strength 1,080 MPa withstands extreme cyclic shock and high mold-locking pressures |
| Food, dairy, pharma & chemical plants | CSK or Cap (SS 304/316) | A2-70 / A4-70 | ASTM A967 passivated | Total metallurgical resistance to washdown CIP detergents, organic acids, and steam sterilization |
| Coastal solar MMS mounting rails | Socket Cap (DIN 912) | A4-70 / A4-80 (316) | Passivated | Molybdenum-bearing SS 316 resists atmospheric marine chloride pitting; pairs with SS 316 spring nuts |
Flush Clearance Requirement
If the joint sits directly beneath a moving tool slide, bearing runner, or mated gasket surface, specify DIN 7991 countersunk screws. Ensure the mating hole is countersunk at 90° with a depth toleranced so the screw head crown sits 0.1 mm below flush.
Maximum Joint Preload & Torque
Where dynamic vibration and heavy shear loads require high clamp preload, specify DIN 912 socket cap screws in Class 10.9 or 12.9. The tall cylindrical head permits full hex engagement depth, handling 40% more tightening torque than button heads.
Space & Snag-Free Guards
On exposed machine covers, electrical cabinets, and operator consoles where operators or cables could catch on sharp corners, specify DIN 7380 button head screws in zinc-plated 8.8 or polished SS A2.
Industrial applications: tool-room, machinery & structural uses
From precision CNC machine centers to corrosive marine solar structures, socket fasteners provide dependable clamp security across diverse industrial environments.
Machine Building & CNC Equipment
DIN 912 socket head cap screws in Property Classes 10.9 and 12.9 are standard in machine tool assemblies, hydraulic manifold blocks, and linear guide carriages where high tightening torque and fatigue resistance are non-negotiable.
Tool & Die and Injection Moulds
Tool-and-die shops rely on Grade 12.9 alloy steel socket cap screws and DIN 916 socket set screws for punch holders, stripper plates, and injection mould cavities enduring continuous stamping shock and thermal cycling.
Jigs, Fixtures & Countersunk Assemblies
DIN 7991 countersunk Allen bolts sit flush within 90° machined countersinks on tooling fixtures, sliding ways, and conveyor wear plates, eliminating head interference during workpiece loading and clamping.
Automation, Robotics & Enclosures
DIN 7380 button head screws in metric sizes M3 to M8 provide clean aesthetics and low catch hazards on robotic arms, aluminum extrusion frames, control panel doors, and electronic equipment chassis.
Food, Dairy & Pharma Processing
Austenitic stainless steel socket cap and CSK screws in SS 304 (A2-70) and SS 316 (A4-70) passivated to ASTM A967 provide corrosion resistance and hygienic cleanability in washdown food processing and pharmaceutical equipment.
Solar MMS & Specialized Sub-Assemblies
Stainless steel A4-70 socket cap screws serve as heavy-duty clamp fasteners on coastal solar mounting structures, strut channels, and scaffolding hardware sub-assemblies requiring guaranteed chloride resistance.
Related industrial fasteners & companion hardware
Consolidate your hardware procurement by pairing CSK Allen bolts with companion nuts, washers, high-tensile anchors, and custom drawing-machined hardware.
Hex Bolts & Nuts
Complete range of commercial and high-tensile hexagon bolts (DIN 931/933), standard nuts (DIN 934), and heavy hex hardware for companion assembly.
matching hex nuts and washers
High-Tensile Fasteners
Metallurgical properties, proof loads, and tempering standards for quenched and tempered carbon and alloy steel fasteners.
PC 10.9 / 12.9 decision guide
Stainless Steel Fasteners
Austenitic stainless steel fasteners in Grades 304 and 316 for chemical, coastal solar, and food processing applications.
SS A2 vs SS A4 for service
Automotive & Heavy Engineering
Precision fasteners and socket screws engineered for commercial vehicle chassis, gearboxes, engine mounts, and heavy mining plant.
automotive and heavy machine assemblies
Custom Fasteners
In-house manufacturing for non-standard shoulder bolts, stepped socket studs, and bespoke alloy hardware machined to engineering drawings.
custom drawing-based socket screwsFrequently asked questions: CSK Allen bolts & socket screws
Common technical inquiries regarding socket head standards, property classes, corrosion finishes, and procurement logistics.