ISO 4579:2021

Overview - ISO 4579:2021 (TORX® PARALOBE® drive for aerospace)

ISO 4579:2021 specifies the geometrical definition, gaging and technical requirements for TORX® PARALOBE® recesses used in aerospace fasteners. The standard defines basic recess configuration, metric and inch recess dimensions, inspection/gaging methods and a fastener recess torque test procedure. It is intended for designers, manufacturers and quality personnel working with aerospace fastener drive systems. Note: TORX® PARALOBE® is a trademark and the standard notes possible patent licensing considerations.

Key topics and technical requirements

• Scope and terminology: Definitions for recess, driver bit, configuration and optimum recess torque.
• Recess geometry and dimensions: Detailed tables of recess diameters and inscribed diameters for drive sizes (drive codes 001–110 SI) given in both metric and inch units.
• Gaging and inspection:
  • Uses a penetration-type go/no‑go gage assembly (go and no‑go elements) to check recess depth and fit.
  • Gage identification, zero check on a flat surface, insertion and depth measurement procedures are specified.
  • Element diameters for each drive size are listed (see Table 2 in the standard).
• Fastener recess torque testing:
  • Test fixture requirements: alignment with fastener axis, non-rotation of fastener, and ability to apply specified end load while not preventing cam-out.
  • Torque device requirements: hand torque wrenches or torsion machines per applicable requirements.
  • Driver bits must conform to ISO 4580.
  • Test procedure: fixture the fastener, align driver bit within 1° of axis, apply end load per NASM1312-25, apply torque in install and removal directions and record results.
  • Optimum recess torque values: Table 3 provides minimum torsional strength/optimum torque values by drive size.

Practical applications and users

Who uses ISO 4579:2021:

• Aerospace fastener designers and engineers specifying internal drive recesses.
• Fastener manufacturers and tooling suppliers ensuring dimensional and functional conformity to TORX® PARALOBE® geometry.
• Quality control and inspection teams using go/no‑go penetration gages for acceptance testing.
• Maintenance, assembly and procurement teams selecting appropriate driver bits and torque requirements for installation/removal operations.

Practical benefits:

• Ensures interchangeability of driver bits and fasteners.
• Provides standardized inspection and torque-test methods to reduce drive failures and cam‑out.
• Supports certification and traceability in aerospace manufacturing and maintenance.

Related standards

• ISO 4580 - driver bit geometry, gaging and technical requirements for TORX® PARALOBE® bits.
• NASM1312-25 - driving recess torque quality conformance test (referenced for end‑load and test details).

Keywords: ISO 4579:2021, TORX PARALOBE, aerospace fasteners, recess dimensions, gaging, go/no‑go gage, torque test, driver bit.