ISO 4579-2021 PDF

Full title and description

ISO 4579:2021 — Aerospace — Drives, internal, TORX® PARALOBE® drive — Geometrical definition, gaging and technical requirements. This international standard specifies the geometric definitions, gauging (gaging) methods and engineering requirements for TORX® PARALOBE® internal drive recesses used in aerospace fasteners.

Abstract

ISO 4579:2021 defines the basic dimensions, form and tolerances, inspection/gaging methods and related technical requirements for internal TORX® PARALOBE® recesses in aerospace fasteners. The standard ensures consistent geometry and interchangeability of recesses, supports appropriate gaging practice for production and inspection, and complements the companion driver-bit specification (ISO 4580:2021).

General information

• Status: Published (current international standard)
• Publication date: 5 November 2021
• Publisher: International Organization for Standardization (ISO)
• ICS / categories: 49.030.01 — Fasteners in general
• Edition / version: Edition 1 (2021)
• Number of pages: 7

Scope

ISO 4579:2021 applies to internal TORX® PARALOBE® drive recesses in aerospace fasteners. It sets out the geometrical definition, nominal dimensions and tolerances, recommended gaging (gauging) configurations and acceptance criteria necessary for manufacture and inspection. The standard is intended to ensure functional interchangeability between fasteners and mating driver bits used in aerospace assemblies and related high-reliability applications.

Key topics and requirements

• Geometrical definition of the TORX® PARALOBE® internal recess (profile, lobes and radii).
• Nominal dimensions and dimensional tolerances for each specified size/designation.
• Gaging (gauging) methods and gauge configurations for production inspection and acceptance checks.
• Requirements for fit and functional engagement with driver bits (reference to complementary driver-bit standard).
• Criteria for permissible wear and acceptable limits for re-use/inspection.
• Guidance for manufacturing and inspection to ensure repeatability and interchangeability in aerospace use.

Typical use and users

Primary users are aerospace fastener manufacturers, tool and bit manufacturers, quality/inspection engineers, procurement/specification teams in aerospace OEMs and suppliers, and maintenance/overhaul organisations. The standard is used to design, produce and inspect internal TORX® PARALOBE® recesses to ensure reliable torque transfer, reduced cam‑out and consistent tool engagement in high-reliability assemblies.

Related standards

Key related documents include ISO 4580:2021 (Aerospace — TORX® PARALOBE® driver bit — geometrical definition, gaging and technical requirements) and earlier SAE aerospace specifications for the TORX® PARALOBE® family (for example SAE AS8538 and SAE AS8539). Related ISO fastener and drive-series standards (hexalobular/torx family and fastener tolerancing documents) provide complementary requirements for fastener designs and tolerances.

Keywords

TORX, PARALOBE, internal drive, recess, gaging, gauging, geometrical definition, fasteners, aerospace, drive profile, tolerances, inspection, driver bit, ISO/TC 20/SC 4

FAQ

Q: What is this standard?

A: ISO 4579:2021 is an international standard that defines the geometry, dimensional tolerances and gaging/inspection requirements for internal TORX® PARALOBE® drive recesses used in aerospace fasteners.

Q: What does it cover?

A: It covers the geometrical definition of the recess profile, nominal sizes, tolerances, recommended gaging arrangements and acceptance criteria to ensure correct engagement with driver bits and reliable torque transfer in aerospace applications.

Q: Who typically uses it?

A: Aerospace fastener manufacturers, tool/driver-bit makers, quality and inspection engineers, procurement/specification teams at OEMs and suppliers, and maintenance/overhaul organisations that require standardised drive recess geometry for high-reliability assemblies.

Q: Is it current or superseded?

A: ISO 4579:2021 was published on 5 November 2021 and is the first edition. It is published/active; no superseding ISO edition is indicated as of 1 March 2026. Users should verify the current status before relying on the standard for new specifications.

Q: Is it part of a series?

A: Yes. ISO 4579:2021 is paired with ISO 4580:2021, which specifies driver-bit geometry and gaging for TORX® PARALOBE® bits. The ISO documents align with prior SAE TORX® PARALOBE® aerospace specifications and with other ISO fastener drive standards in the hexalobular/TORX family.

Q: What are the key keywords?

A: TORX PARALOBE, internal drive, recess, gaging/gauging, geometrical definition, aerospace fasteners, driver bit, tolerances, inspection.