ISO 12257:2008

Overview

ISO 12257:2008 is an international standard published by the International Organization for Standardization (ISO) that specifies the dimensions for metric internal six-lobe drives commonly used in aerospace fastener systems. This standard applies to internal six-lobe (also known as Torx) drive profiles integrated into metric screws with nominal thread diameters ranging from 3 mm to 20 mm. The document ensures consistent geometric and dimensional characteristics for aerospace applications, promoting interchangeability and precision in manufacturing and assembly.

The standard plays a crucial role in aerospace engineering by defining exact tolerances and geometric parameters essential for the reliability and safety of aerospace fasteners, where high torque transmission and secure fastening are critical.

Key Topics

• Metric Internal Six-Lobe Drives: Specifies the shape and size of six-lobe drive profiles used internally in screws.
• Nominal Thread Range: Covers screws with nominal thread diameters from 3 mm up to 20 mm.
• Dimensional Specifications: Includes detailed dimensions such as the drive code, depth, width, and other profile specifics with precise millimetre tolerances.
• Geometrical Tolerancing: Conforms to ISO 1101 standards for form, orientation, location, and run-out tolerances, ensuring precise manufacturing.
• Drive Designation: Defines the labeling system for internal six-lobe drives to standardize identification across products.
• Optional Chamfer: Allows for an optional chamfer at the drive entry for improved tool engagement, enhancing manufacturing flexibility.
• Safety and Compatibility: By standardizing drive dimensions, ISO 12257 helps avoid cross-compatibility issues and potential failures in aerospace fastener applications.

Applications

ISO 12257:2008 is essential in advanced aerospace sectors where secure, high-torque fastening solutions are necessary. Its applications include:

• Aircraft Assembly: Used in fastening components where reliability and torque transmission precision are critical to structural integrity.
• Space Vehicles: Ensures consistent fastener profiles for components subjected to extreme conditions in aerospace and space exploration.
• Manufacturing of Aerospace Fasteners: Guides screw manufacturers in producing internal six-lobe drive screws that meet global aerospace quality and dimensional standards.
• Maintenance and Repair: Facilitates identification and replacement of screws and drives, supporting maintenance operations with standardized parts.
• Quality Control and Inspection: Provides measurement criteria that manufacturing and inspection teams use to verify compliance and avoid defects.

Related Standards

• ISO 1101 – Geometrical Product Specifications (GPS) - Geometrical tolerancing including tolerances of form, orientation, location, and run-out. Used as a normative reference within ISO 12257:2008 to apply precise tolerancing.
• Other aerospace fastener standards maintained by ISO/TC 20/SC 4, which encompass related specifications for screw threads and fastener systems used in aerospace vehicles.
• Industry-specific standards for metric screws and drives that align with or complement ISO 12257, ensuring widespread compatibility and safety.

Adhering to ISO 12257:2008 ensures aerospace manufacturers and fastener producers can consistently produce and utilize metric internal six-lobe drive screws that meet rigorous aerospace requirements. The standard's clear dimensional guidelines and tolerance references streamline design, production, quality assurance, and maintenance processes within aerospace engineering sectors.