Hex Socket Countersunk Head Screws

DIN 7991 Stainless Steel Countersunk Socket Screws for Flush Machinery & Equipment Assembly

DIN 7991 Hex Socket Countersunk Head Screws combine a 90° flat countersunk head, internal hex drive and machine thread for assemblies requiring a flush or near-flush surface. DIN 7991 remains a widely used purchasing designation; the current corresponding reference is DIN EN ISO 10642:2026 / ISO 10642:2026.

Primary Standard

DIN 7991

Current Reference

DIN EN ISO 10642:2026 / ISO 10642:2026

Head / Drive

90° Countersunk / Internal Hex

Thread

Machine Thread

DIN Market Range

M3–M24

Common Length

Approx. 8–100 mm

Materials

304 / A2 and 316 / A4 Stainless Steel; Carbon and Alloy Steel

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Product Overview

DIN 7991 combines a 90° countersunk head, hex socket and machine thread. It enters an existing tapped hole, nut or threaded insert and is selected where external projection must be minimized, equipment clearance is limited and hex-key installation is preferred.

Correct alignment between the 90° head and mating countersink supports flush seating and intended bearing contact. Because the shallow head also contains the internal socket, current ISO 10642 defines this family with reduced loadability; the head is a critical limiting section.

For quotations, specify DIN 7991 or ISO 10642, diameter, pitch, overall length, material, property requirement, head and socket geometry, full or partial thread, finish, mating thread, quantity and drawing where necessary.

Technical Specifications

Product

Hex Socket Countersunk Head Screws

Primary Purchasing Designation

DIN 7991

Current German / International Reference

DIN EN ISO 10642:2026 / ISO 10642:2026

Head / Drive / Thread

Flat 90° countersunk head / internal hex socket / machine thread

Traditional DIN 7991 Market Range

M3–M24 according to customer specification

Current ISO 10642:2026 Scope

M2–M20, metric coarse thread, product grade A

Main Commercial Sizes

M4 / M5 / M6 / M8 / M10 / M12 / M16

Length

Common commercial range approximately 8–100 mm; longer sizes up to approximately 200 mm for suitable larger diameters and specifications

Length Measurement

Overall length L is measured from the top of the countersunk head to the screw end

Materials / Finish

304 / A2, 316 / A4, carbon steel and alloy steel; finish according to material and order

Key Dimensions

d, P, L, b, dk, k, 90° head angle, hex socket s and socket depth t

90° Countersunk Fit, Hex Socket & Reduced Loadability

Correct Alignment

A compatible 90° countersink supports proper flush or near-flush seating and intended bearing contact.

Proud / Excessive Seating

A shallow, oversized or mismatched countersink can leave the head proud, too deep or supported by localized contact.

Overall Length L

Measure from the top of the countersunk head to the screw end, not from beneath the head.

Hex Socket Engagement

Use the correct hex key with full engagement and alignment to reduce rounding, slip and recess damage.

Why Loadability Is Reduced

The shallow countersunk head and penetrating socket leave less material in the critical head section than a full-height socket head.

ISO 10642 Loadability Concept

For current standardized ISO 10642 configurations, head loadability is approximately 80% of thread loadability; this must not be generalized to every custom geometry or material.

DIN 7991 vs DIN 912

DIN 7991 provides a flat flush 90° countersunk head with reduced head loadability; DIN 912 / ISO 4762 uses a taller cylindrical socket head above the surface and must not be treated as mechanically interchangeable.

Stainless Steel, Steel & Size Options

1304 / A2 Stainless Steel — Major VALTOR option for machinery, equipment, fixtures and general corrosion-resistant assemblies.

2316 / A4 Stainless Steel — Increased corrosion resistance for compatible humid, outdoor, coastal and industrial environments.

3Carbon / Alloy Steel — Available with applicable property class and finish, including 8.8, 10.9 or 12.9 where the actual specification permits.

4Separate Size Scopes — DIN market supply M3–M24; current ISO 10642:2026 scope M2–M20. These ranges are not interchangeable.

Thread, Length & OEM Manufacturing

Thread Options

Metric coarse is primary. Metric fine and special metric threads may be supplied by drawing. UNC / UNF products are custom or applicable inch-standard products, not standard DIN 7991 metric products.

Full / Partial Thread & Length

Thread coverage and length depend on diameter, applicable standard and requirement. Common lengths are 8–100 mm; extended lengths are qualified by diameter and feasibility.

OEM Input

Provide standard, diameter, pitch, length, material, property requirement, full/partial thread, countersink, finish, quantity and drawing or sample.

Packaging

Inner bags, boxes, export cartons, wooden pallets, customer labels, part numbers and authorized private-label packaging.

Head, Socket & Dimensional Quality

✓

Thread Profile & GO / NO-GO Fit

✓

Top-of-Head Overall Length

✓

90° Head & Bearing Surface

✓

Hex Socket Size & Depth

✓

Head / Socket Concentricity

Inspection may verify diameter, pitch, continuity, overall length, head diameter and height, 90° geometry, socket engagement, material and applicable mechanical requirements. Representative countersink checks can review flushness and bearing contact. Documentation may include MTC, raw-material, dimensional, thread and actually performed mechanical test reports without inventing universal torque or load values.

Applications

Flush internal-hex fastening for accurately countersunk machinery and equipment components.

DIN 7991 stainless steel countersunk socket screw installed flush in industrial machinery

Machinery Covers & Flush Surfaces

Internal-hex fastening where covers require minimal head projection.

Automation Equipment

Brackets, guides and frames where head clearance is important.

Fixtures & Tooling

Jigs and machined components requiring repeatable countersunk seating.

Equipment Panels & Brackets

Thicker panels and brackets designed with compatible 90° countersinks.

OEM Mechanical Components

Drawing-controlled DIN 7991 or ISO 10642 style assemblies.

Frequently Asked Questions

What is DIN 7991?

DIN 7991 is a widely used purchasing designation for 90° Hex Socket Countersunk Head Screws with machine thread. The original DIN standard has been withdrawn, but the designation remains common in purchasing and machinery drawings.

What is the difference between DIN 7991 and ISO 10642?

ISO 10642 is the current international standard family, while DIN 7991 remains the common legacy purchasing designation. Current ISO 10642:2026 covers M2–M20; traditional DIN market references commonly extend M3–M24. Confirm the required standard because dimensions are not automatically interchangeable.

Why does DIN 7991 / ISO 10642 have reduced loadability?

The shallow countersunk head and central hex socket reduce the remaining head cross-section compared with a full-height socket head, making the head a limiting section.

What sizes can VALTOR supply?

Common DIN 7991 market supply is approximately M3–M24 with typical 8–100 mm lengths; longer versions depend on diameter and specification. Strict current ISO 10642:2026 orders use its M2–M20 scope.

Should I use DIN 7991 or DIN 912?

Choose DIN 7991 for a designed 90° countersink and flush surface. DIN 912 uses a taller cylindrical socket head above the surface. Their head geometry and loadability differ, so joint design must be reviewed.