# Socket-head cap screws

Hex socket geometry, metric and inch designations, head variants, and source-specific material and strength limits.

Reviewed: 2026-10-30

Tags: components, fasteners, screws

NBK's **SNS-M6-20** and **SSH-M6-20** both list **M6 × 1**, **20 mm** length and **10 mm** head diameter. The standard SNS has a **6 mm** head and **5 mm** socket, with class **12.9**. The ultra-low SSH has a **1.5 mm** head and **3 mm** socket, with reference thread and head strengths **10.9 and 5.8** for M2–M8. Check each head and drive for the joint. [NBK SNS-M6 table and material section](https://static.nbk1560.com/en-US/products/specialscrew/nedzicom/high_specific_strength/SNS-J/SNS-M6/), [NBK SSH-M6 table and material section](https://www.nbk1560.com/en-US/products/specialscrew/nedzicom/socketheadcapscrew/SSH/SSH-M6/?SelectedLanguage=en-US).

## Identity and geometry

The drive is an internal hexagon. Verify the actual head form and socket depth. [NBK, socket-head cap screws](https://www.nbk1560.com/en/products/specialscrew/nedzicom/socketheadcapscrew/?screw_length=16).

SPS dimensions head height, socket depth, threaded length and transition separately. [SPS Technologies, socket brochure, pp. 7, 20](https://www.pccfasteners.com/assets/local/documents/product-literature/socket_brochure.pdf).

## Dimensional families and editions

| Reference | Publicly documented scope and edition | Boundary |
| --- | --- | --- |
| ISO 4762:2004 | Edition 4, published March 2004; coarse-pitch hexagon socket-head cap screws, M1.6 through M64, product grade A. ISO reports confirmation in 2023. | The public abstract identifies scope; it does not expose the full dimensional tables or all requirements. [ISO record](https://www.iso.org/standard/34460.html) |
| DIN 912:1983-12 | DIN Media identifies the December 1983 document as a modified version of ISO 4762 and marks it withdrawn. | Its replacement record names DIN EN ISO 4762:1998-02 and :2004-06. A replacement relationship alone does not establish identical dimensions across editions. [DIN Media record](https://www.dinmedia.de/de/norm/din-912/1078263) |
| ASME B18.3-2026 | ANSI's ASME record lists the inch-series standard for socket cap, shoulder and set screws, plus hexagon and spline keys; it revises B18.3-2012. | The public description covers dimensional data and gaging/key information. It does not establish that every listed size is a stocked product. [ANSI/ASME record](https://webstore.ansi.org/standards/asme/asmeb182026) |

NBK lists SNS-J as complying with JIS B 1176, ISO 4762 and DIN 912, without editions on the product page. That is a manufacturer's product statement; it does not resolve every difference among the cited editions. [NBK, SNS-M6](https://static.nbk1560.com/en-US/products/specialscrew/nedzicom/high_specific_strength/SNS-J/SNS-M6/)

## Named metric examples

The following are NBK catalog fields in millimeters. L, D₁, L₁ and B are the manufacturer’s catalog symbols; these fields do not constitute complete toleranced product drawings.

| Named product | Thread and pitch | L | D₁ | L₁ | B | Material/finish and stated strength |
| --- | --- | --- | --- | --- | --- | --- |
| SNS-M6-20, standard profile | M6 coarse; pitch 1 | 20 | 10 | 6 | 5 | SCM435; black ferrosoferric oxide film; strength class 12.9. [NBK SNS-M6 table and material section](https://static.nbk1560.com/en-US/products/specialscrew/nedzicom/high_specific_strength/SNS-J/SNS-M6/) |
| SSH-M6-20, ultra-low profile | M6 coarse; pitch 1 | 20 | 10 | 1.5 | 3 | SCM435; black ferrosoferric oxide coating; thread strength class 10.9 and head strength class 5.8 for M2–M8. [NBK SSH-M6 table and material section](https://www.nbk1560.com/en-US/products/specialscrew/nedzicom/socketheadcapscrew/SSH/SSH-M6/?SelectedLanguage=en-US) |

For SSH, NBK explicitly describes head height as 1.5 mm or less, states that head strength is lower than thread strength, and labels chart values as reference values rather than guaranteed values. Thus, in this pair, equal nominal thread, pitch, length field and D₁ coexist with different L₁, B and strength designations. This comparison demonstrates why a lower profile does not imply the standard-profile product's mechanical properties. [NBK, SSH-M6](https://www.nbk1560.com/en-US/products/specialscrew/nedzicom/socketheadcapscrew/SSH/SSH-M6/?SelectedLanguage=en-US)

## Inch threads and other head forms

In SPS's 1960-series .250-20 UNRC-3A row, head diameter is .365–.375 in., head height .244–.250 in. and nominal socket width .188 in. Thread class and socket width are distinct from nominal thread size. [SPS, p. 7](https://www.pccfasteners.com/assets/local/documents/product-literature/socket_brochure.pdf)

SPS distinguishes reduced cylindrical low heads, rounded button heads and conical 82° flat heads. Their head and seating geometry differ despite the shared hexagonal recess. [SPS, pp. 14, 18, 20](https://www.pccfasteners.com/assets/local/documents/product-literature/socket_brochure.pdf)

## Material, mechanical properties and joint behavior

ASTM A574-21 addresses quenched-and-tempered alloy-steel hexagon socket-head cap screws, with a public scope of 0.060 through 4 in. diameter and inch-pound units. Its abstract names tensile/wedge strength, proof load, yield strength, elongation and hardness testing. This is a material and mechanical-requirements reference, whereas ASME B18.3's public description addresses general and dimensional data. Neither a hexagonal recess nor a shared head style establishes A574 conformity. The ASTM page identifies the edition as A574-21 and its page update as November 17, 2023; these are different dates. [ASTM A574-21, public abstract and scope](https://store.astm.org/standards/a574), [ANSI/ASME B18.3-2026](https://webstore.ansi.org/standards/asme/asmeb182026)

SPS identifies mating material, plating, lubrication, surface finish, hardness, joint compliance and tightening method as variables affecting induced load. Its torque tables therefore do not establish a universal torque-to-preload relationship. [SPS, p. 6](https://www.pccfasteners.com/assets/local/documents/product-literature/socket_brochure.pdf)

## Coverage and source limits

The NBK examples are undated public catalog entries accessed October 30, 2026 PDT; their visible product pages provide no controlled drawing revision. Their material, finish and strength statements apply to the named series. The public ISO, DIN, ASME and ASTM records support the edition and scope distinctions above; full standards were not consulted.

The SPS brochure footer identifies ©2005 and code 5525Rev3, 03/05. Its historical product examples do not establish current supply or qualification. [SPS, p. 36](https://www.pccfasteners.com/assets/local/documents/product-literature/socket_brochure.pdf) The sources here do not establish joint load capacity, fatigue life, reuse limits, an installation torque or a customer's approved fastener configuration.

## Related reference

[Hardware and component references](../index.md)