Button-head screws

Accu's SSB-M6-20-A2 lists a 10.5 mm maximum head diameter, 3.3 mm head height and 4 mm hex socket. Its A2 label identifies stainless material. The listing gives no A2 property class. ISO 7380 public abstracts describe reduced head loadability and an 80% of thread loadability assumption for the covered forms. Check the exact head and drive before using a strength or torque limit. Accu product SSB-M6-20-A2, technical specification, ISO 7380-1:2022 abstract.

Identity and geometry

A button-head screw has a low, rounded head above the bearing surface, as described for Accu’s socket-button range. Accu product description.

The button head is a rounded profile. Specify the drive, thread, material and collar separately. ISO 7380-1:2022, ISO 7380-2:2022, ISO 7380-3:2026, ISO 7380-4:2026.

Use head diameter and height for envelope checks and socket size and depth for drive clearance. Accu product SSB-M6-20-A2, technical specification.

Specified forms

ISO 7380-2:2022 and ISO 7380-4:2026 both state steel in their scope. The public part 2 abstract names ISO 888 and ISO 4753 for dimensional options; the part 4 abstract additionally names ISO 898-1 or ISO 3506-1 when other property classes or stainless-steel grades are requested. This difference matters: neither abstract establishes the material and mechanical properties of a particular catalog item. ISO 7380-2:2022 abstract, ISO 7380-4:2026 abstract.

Dimensions and mechanical limits

One product-specific example is Accu's M6 × 20 mm socket button screw, product SSB-M6-20-A2, listed as ISO 7380-1 and stainless steel A2. Its HTML technical specification gives a 10.5 mm head diameter (maximum, +0/−0.43 mm tolerance), 3.3 mm head height (listed as “Head Length (H)”, +0/−0.3 mm tolerance), 4 mm socket size, 2.08 mm minimum socket depth, and 1 mm thread pitch. These are supplier-listed values for that product, not a complete ISO dimensional table or a universal button-head specification. Accu labels the head and drive dimensions D, H, J, and P, respectively. Accu product SSB-M6-20-A2, technical specification.

The public abstracts for all four cited ISO 7380 parts describe reduced ultimate tensile loadability from the specified head dimensions combined with socket penetration. They describe a standard-specific assumption that head loadability is 80% of thread loadability and a property-class marking preceded by zero. That figure is not an allowable service load, tightening torque, fatigue rating, or universal reduction factor for other head designs. The complete standard's tables and test requirements are outside the public abstract used here. ISO 7380-1:2022 abstract, ISO 7380-2:2022 abstract, ISO 7380-3:2026 abstract, ISO 7380-4:2026 abstract.

Thread size and pitch, length and thread extent, material grade, property class, finish, head form, and drive remain separate attributes. The Accu example explicitly lists M6 × 20 mm, 1 mm pitch, A2 stainless steel, natural finish, hexagon socket size, and the ISO 7380-1 form; it does not state a stainless property class such as A2-70. Thus an A2 material label cannot silently supply an unstated property class, and an unqualified ISO 7380-1 label cannot establish a particular finish or thread extent. Accu product SSB-M6-20-A2, technical specification, ISO 7380-1:2022 abstract.

Related head forms and fit

A pan head is a different head form: ISO 14583:2011 identifies hexalobular socket pan-head screws with M2–M10 threads. ISO 14583:2011 abstract.

ISO 4762:2004 identifies hexagon socket-head cap screws. For a supplier example of their cylindrical head form, Bossard lists BN 1057 with a cylindrical head and hexagon socket. That listing is polyamide PA 6.6 and marks its standard association ~ISO 4762; it supports the head-form comparison, not a claim of steel-fastener properties or full ISO 4762 conformance. ISO 4762:2004 abstract, Bossard BN 1057, product attributes.

ISO 10642:2026 identifies a separate reduced-loadability countersunk form and specifically calls out alignment of the head with the countersink's bearing surface. Synthesis: its seating geometry differs from a projecting button head. These references establish distinct geometry categories, not dimensional or mechanical interchangeability. ISO 10642:2026 abstract.

Synthesis: selection for an assembly depends on the drawing's head and recess envelope, bearing surface, accessible driver, mating thread and engagement, material/finish environment, and required joint performance. The cited public abstracts and supplier product pages do not establish a universal torque, preload, safe working load, or permission to substitute one head form or drive for another. Application-specific joint design and the actual fastener specification supply those values and constraints.

Source coverage

The ISO links above are publisher pages for the stated editions and public abstracts, not access to the complete purchased standards. The Accu citation is the HTML technical specification of product SSB-M6-20-A2; its listed dimensions and material designation apply to that listing. Bossard BN 1057 supplies only the cylindrical-head comparison for its PA 6.6, approximately ISO 4762-related listing. Neither supplier page is a substitute for the complete ISO standard.

Accu's component history labels the specification “Specification Last Updated.” Retained page snapshots inspected on 30 October 2026 PDT showed 24 October 2026 and 30 October 2026 under that label; a further retrieval that day also showed 30 October. The cited technical fields were unchanged across these snapshots. These are variable supplier specification-update dates, separate from the retrieval and article-review date; they do not identify a controlled product edition or establish a change to the fastener itself. The retrieved HTML text can reflect indexed or cached content rather than a live response from the supplier. Accu product SSB-M6-20-A2, Component History and Technical Specification.

This article was reviewed on 30 October 2026 PDT. It does not claim current stock availability, conformance of a particular lot, a manufacturer's process capability, or a customer's approved hardware.