ISO 5855-2:1999

Overview

ISO 5855-2:1999 is an international standard developed by the International Organization for Standardization (ISO) specific to aerospace applications. This standard defines the limit dimensions for MJ threads used in bolts and nuts with nominal diameters ranging from 1.6 mm up to 39 mm. It provides precise dimensional requirements to ensure reliable fastening components for aerospace constructions.

Part 2 of ISO 5855 focuses on the dimensional limits for thread profiles, guaranteeing compatibility, safety, and performance in critical aerospace environments. The standard is a revision and technical update of the previous edition from 1988.

Key Topics

• Scope: Applies to MJ thread bolts and nuts for aerospace use, specifying limit dimensions essential for mechanical integrity.
• Nominal Diameter and Pitch: Covers diameters from 1.6 mm to 39 mm with corresponding thread pitches detailed in tabulated form.
• Tolerance Classes: Defines tolerance grades for threads to maintain precise fit; typically 6H for bolts under 5 mm and 5H/4H for larger diameters.
• Thread Profiles: Depicts maximum and minimum limit profiles for both bolt and nut threads, ensuring standardized engagement.
• Coated Threads: Addresses dimensional considerations for threads before and after coatings, to accommodate thickness and maintain compliance.
• Dimensional Tables: Provides exhaustive tables with detailed outer diameter, flank diameter, root diameter, and pitch radius values.
• Permissible Deviations: Specifies maximum permissible variations in thread pitch and flank angles relevant to manufacturing quality control.

Applications

The ISO 5855-2:1999 standard is integral to the aerospace industry, where fasteners with MJ threads play a critical role in:

• Aircraft assembly and maintenance: Ensuring threaded fasteners meet stringent dimensional tolerances for safety and reliability.
• Spacecraft and satellite construction: Providing secure joints resistant to extreme mechanical stresses and temperature variations.
• Fluid systems connections: Compatibility with fluid sealing components using MJ threads (covered more extensively in other parts).
• Aerospace component manufacturing: Enabling consistent production quality and interchangeability of threaded parts.
• Coated fastener production: Managing dimensional allowances when threads are subjected to plating or other protective treatments.

Related Standards

ISO 5855-2 is part of a broader ISO 5855 series for aerospace MJ threads, including:

• ISO 5855-1:1999 - General requirements for MJ thread design and application.
• ISO 5855-3 - Limit dimensions for MJ thread connections in fluid systems.

For complete thread tolerance principles, ISO 965-1:1998 on Metric ISO General Purpose Threads is referenced for fundamental tolerancing guidelines.

Together, these standards form a comprehensive framework supporting safe, interoperable, and high-precision threaded fasteners tailored for the demanding aerospace sector.

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