Stainless Steel Socket Head Cap Screws: DIN 912, A2-70, A4-80 and Sizes Buyer Guide

Socket head cap screws are among the most widely used stainless steel fasteners in machinery, equipment and precision assembly. Their cylindrical head with an internal hex drive lets you tighten them in tight spaces where a hex bolt would not fit, and they offer higher clamp load than standard machine screws. This guide covers the standards, grades, dimensions and selection criteria buyers need when specifying stainless steel socket head cap screws for an RFQ.

What is a socket head cap screw?

A socket head cap screw (SHCS) is a threaded fastener with a cylindrical (button-style) head and an internal hexagon recess — commonly called an Allen socket — that is driven with a hex key (Allen wrench). Unlike hex bolts, which have an external hex head turned with a spanner, socket cap screws are installed from the top side using a hex key inserted into the head.

The design originated in Germany under DIN 912 and was later adopted as ISO 4762. In North America, the equivalent inch-series standard is ASTM A574 / ASME B18.3. The head is designed to fit into a counterbore, giving a flush or recessed finish that looks cleaner and eliminates protrusions that could catch on moving parts.

1. Standards: DIN 912, ISO 4762 and ASTM A574

When you request socket head cap screws, confirm which standard your fabricator or assembly expects. The most common references are:

DIN 912 — the classic German metric standard, widely specified in European and Asian engineering drawings. Covers M1.6 to M64 diameters.
ISO 4762 — the international equivalent of DIN 912; dimensions are nearly identical, and most manufacturers supply to both.
ASTM A574 / ASME B18.3 — inch-series socket head cap screws (1/4 in to 1-1/2 in), used in North American machinery and equipment.

For most global buyers sourcing from China, India or Southeast Asia, DIN 912 / ISO 4762 metric screws are the default. If your drawing says “DIN 912,” the supplier will cut a metric thread (M series). If it references A574, expect Unified inch threads (UNC/UNF). Mixing the two on one assembly is a common sourcing mistake — always specify the thread series clearly on the RFQ.

2. Material grades: A2-70 vs A4-80

Stainless steel socket head cap screws are most commonly supplied in austenitic grades. The two workhorses are:

A2-70 (AISI 304) — general-purpose stainless. Good corrosion resistance in indoor, dry or mildly humid environments. “70” means the minimum tensile strength is 700 MPa. Suitable for food equipment, furniture, architectural trim and machinery housings.
A4-80 (AISI 316) — molybdenum-bearing stainless for corrosive environments. “80” means 800 MPa minimum tensile. Specify A4-80 for coastal installations, marine hardware, chemical processing, wastewater equipment and outdoor fixtures exposed to rain or salt spray.

For a deeper comparison of the two grades, see our guide on A2-70 vs A4-80 stainless fastener grades. The grade marking appears on the top of the head or on the box label — always ask the supplier to confirm the grade and provide a mill test certificate (MTC) for critical applications.

3. Key dimensions buyers must specify

When sending an RFQ for socket head cap screws, include all of the following so the supplier ships the correct part the first time:

Diameter (thread size) — e.g., M6, M8, M10. The “M” denotes a metric coarse thread pitch unless a fine pitch is specified (e.g., M8×1.0 instead of standard M8×1.25).
Length — measured from under the head to the tip of the screw. For socket cap screws, the head height is NOT included in the length. An M8×20 means an M8 screw with 20 mm of shank under the head.
Head diameter and height — governed by the standard. For M8 DIN 912, head diameter is ~13 mm and head height is ~8 mm. These are not usually negotiated; they follow the standard.
Hex key (Allen) size — determined by diameter. M6 uses a 5 mm hex key, M8 uses 6 mm, M10 uses 8 mm, M12 uses 10 mm. Buyers often order matching hex keys alongside.
Thread length — for longer screws, specify whether you want fully threaded or partially threaded. Standard DIN 912 screws up to a certain length (typically M8×40 and shorter) are fully threaded; longer screws have an unthreaded grip portion under the head.
Property class — A2-70 or A4-80 as above.

4. Common size range and typical uses

The most requested socket head cap screw sizes for B2B buyers are:

M3, M4, M5 — electronics, instrument panels, small equipment, 3D printers and fixtures.
M6, M8, M10 — the workhorse range for machinery, conveyor systems, machine guards, furniture and automotive aftermarket parts.
M12, M16, M20 — heavy machinery, structural brackets, pump assemblies and equipment skids.

Socket head cap screws are preferred over hex bolts whenever space above the joint is limited — the cylindrical head drops into a counterbore so the surface sits flush. They are also favored in applications where a low-profile, clean appearance matters, such as food-grade equipment and architectural fixtures.

5. Advantages and limitations

Advantages:

Low head profile — fits counterbored holes for a flush finish.
High clamp load — internal hex drive transfers torque efficiently without rounding off the way an external hex can if the spanner slips.
Good appearance — clean, uniform cylindrical heads suit visible equipment surfaces.
Reusable — stainless threads resist galling better than coated steel; with proper lubrication they can be removed and reinstalled.

Limitations:

The internal hex recess can strip if over-torqued or if the hex key is worn. Use the correct key size and a torque wrench for critical joints.
They require access from the top side — if the joint is blind from the top, a hex bolt or threaded stud may be more practical.
Stainless fasteners can gall under high torque; consider anti-seize compound on A4-80 stainless-to-stainless assemblies.

6. Socket head cap screws vs hex bolts

Buyers often ask when to choose a socket head cap screw over a standard hex bolt. The short answer: use a socket cap screw when head space is tight or you want a flush finish; use a hex bolt when you need to tighten from the outside with a spanner or when the joint is accessible only from below. For more on the hex bolt format, see our guide on stainless steel hex bolts and nuts. When assembling with nuts, matching washers improve load distribution — see our flat, spring and lock washer guide for selection.

7. RFQ checklist for buyers

Before sending your inquiry, confirm the following on the drawing or RFQ:

Standard: DIN 912 / ISO 4762 (metric) or ASTM A574 (inch).
Material grade: A2-70 (304) or A4-80 (316).
Diameter and pitch: e.g., M8×1.25 (coarse) or M8×1.0 (fine).
Length: measured under the head.
Thread condition: fully threaded or partially threaded.
Quantity per size and total order quantity.
Surface finish: plain (standard for stainless) or passivated.
MTC requirement: EN 10204 3.1 or equivalent for pressure or safety-critical work.
Packaging: bulk, boxed, or bagged with labels.

Get a quote on stainless steel socket head cap screws

SOROYA supplies DIN 912 / ISO 4762 stainless steel socket head cap screws in A2-70 and A4-80, from M3 to M20, with full mill test certification. Send your drawing or size list and we will quote within one business day.

SOROYA PTE. LTD.
Email: nancy@soroya.com.sg
WhatsApp: +65 8058 3416