ISO 12257-2008 PDF

Full title and description

ISO 12257:2008 — Aerospace — Internal six-lobe drives — Metric series. This international standard specifies the dimensional series and basic geometric requirements for metric internal six-lobe (six‑point) drives used in metric screws intended for aerospace applications, covering nominal thread diameters from 3 mm to 20 mm.

Abstract

ISO 12257:2008 defines the metric series of internal six‑lobe drive recesses (commonly encountered as six‑point/TORX‑style drives) for aerospace fasteners. The document provides the drive designations and the relevant dimensional limits and tolerances required to ensure interchangeability, correct driver engagement and reliable torque transmission in aerospace screw applications.

General information

• Status: Published — valid international standard (confirmed at periodic review).
• Publication date: 21 July 2008 (Edition 1, 2008).
• Publisher: International Organization for Standardization (ISO).
• ICS / categories: 49.030.20 — Bolts, screws, studs (Aerospace fastener systems).
• Edition / version: Edition 1 (2008).
• Number of pages: 2 (concise dimensional specification sheet).

Scope

This standard specifies the dimensions of metric internal six‑lobe drives used in metric screws with nominal thread diameters in the range 3 mm to 20 mm. It establishes the drive size designations and the essential geometric limits for drive recesses intended for aerospace fasteners to promote interchangeability and reliable mechanical engagement between driver and fastener.

Key topics and requirements

• Definition of metric six‑lobe drive series and corresponding drive size designations for nominal screw thread diameters 3 mm to 20 mm.
• Dimensional limits and tolerances for recess geometry (depth, width, clearances) necessary for correct driver engagement.
• Designation and identification conventions for internal six‑lobe drives used on aerospace fasteners.
• Requirements intended to ensure interchangeability and consistent torque transmission characteristics in aerospace assemblies.
• Normative linkage to geometric tolerancing and inspection practice to support quality control (use of general GPS/tolerancing principles).

Typical use and users

ISO 12257:2008 is used by aerospace fastener designers, screw and bolt manufacturers, tool and driver manufacturers, procurement/specification engineers, quality and inspection personnel, and maintenance/repair organizations. It is applied when specifying internal six‑lobe drives on metric aerospace screws to ensure correct manufacture, inspection and driver compatibility.

Related standards

Standards commonly referenced alongside ISO 12257:2008 include ISO standards for geometric product specification and tolerancing (for inspection practices) and other aerospace fastener standards in the ISO/TC 20/SC 4 family. Examples of related fastener/drive standards include ISO 10664 (hexalobular internal driving features), various ISO aerospace screw dimension standards and other internal drive definition documents covering TORX/PARALOBE and cruciform drive series.

Keywords

internal six‑lobe drive, six‑point drive, TORX style, metric series, aerospace fasteners, drive recess dimensions, ISO 12257:2008, fastener geometry, drive designation, drive tolerances

FAQ

Q: What is this standard?

A: ISO 12257:2008 is an international standard that specifies the metric series of internal six‑lobe drive recesses for aerospace screws (nominal thread diameters 3 mm to 20 mm), providing the dimensional definitions and limits for those drives.

Q: What does it cover?

A: It covers the drive size designations and the essential geometric dimensions and tolerances of internal six‑lobe (six‑point) recesses used on metric aerospace screws to ensure interchangeability and reliable driver engagement.

Q: Who typically uses it?

A: Fastener designers and manufacturers, tool and driver producers, aerospace engineers specifying hardware, procurement teams, quality inspectors and maintenance technicians use this standard to ensure correct drive geometry and compatibility.

Q: Is it current or superseded?

A: ISO 12257:2008 is a published international standard (Edition 1, 2008) and was confirmed at periodic review; it remains in force. Work to update or replace it (committee drafts addressing internal drive geometries) has been recorded in ISO technical committee activity, so users should verify the status if a replacement edition has been published after 2008.

Q: Is it part of a series?

A: Yes. ISO 12257:2008 is part of the suite of aerospace fastener standards maintained by ISO/TC 20/SC 4. It is closely related to other internal drive and fastener dimension standards (for example those defining hexalobular drives and other internal drive types) used in aerospace fastener specification.

Q: What are the key keywords?

A: Internal six‑lobe drive, TORX, metric series, aerospace fasteners, drive dimensions, drive tolerances, ISO 12257.