EN 20273:1991

Overview

EN 20273:1991 is a European standard developed by CEN that provides specifications for clearance holes used with bolts and screws. Fully aligned with ISO 273:1979, this standard focuses on defining appropriate diameters for clearance holes to ensure proper fit and mechanical performance in general fastening applications. It covers thread diameters ranging from 1 mm up to 150 mm and categorizes hole diameters according to fine, medium, and coarse thread series. While it primarily addresses general purpose use, the standard advises designers to select hole dimensions tailored to specific applications based on unique design requirements.

Key Topics

• Clearance Hole Diameters
  The standard tabulates specific hole diameters that correspond to various thread sizes and pitch series including fine, medium, and coarse threads. This ensures compatibility and optimal clearance between fasteners and mating components.

• Thread Diameter Range
  EN 20273:1991 covers a broad range of bolt and screw sizes from 1 mm to 150 mm in diameter, making it applicable across many mechanical engineering and manufacturing sectors.

• General vs. Special Applications
  While the standard sets clear guidelines for general fastening use, it highlights that clearance holes for specialized applications should be determined based on precise design parameters, such as load conditions, material properties, and assembly requirements.

• Standard Harmonization
  The document aligns fully with ISO 273:1979, allowing seamless integration for international manufacturing and engineering projects. It also integrates with various national standards across Europe.

Applications

• Mechanical Engineering
  Ensuring correct clearance holes is critical for assembly efficiency and structural integrity of machinery and equipment components.

• Automotive Industry
  Precision in hole sizes for bolts and screws improves reliability and serviceability of vehicle assemblies.

• Construction and Structural Engineering
  Adhering to EN 20273 hole specifications enhances fastening strength and durability in metal frameworks and load-bearing structures.

• Manufacturing Design and Quality Control
  Designers and quality inspectors use this standard to specify and verify hole dimensions during product development and production stages, reducing errors and improving fit.

• Maintenance and Repair
  Standardized clearance hole sizes facilitate replacement of fasteners with compatible components, simplifying maintenance processes.

Related Standards

• ISO 273:1979
  The original international standard for clearance holes which EN 20273:1991 is based upon, ensuring international compatibility.

• EN ISO 898
  Covers mechanical properties of fasteners which complement the hole dimension specifications by defining fastener strength classes.

• EN 1090 Series
  Structural steel and aluminum fabrication standards often reference clearance hole standards for bolted connections.

• National Fastener Standards
  Many European countries have adopted harmonized versions of EN 20273 to maintain consistency across internal and cross-border manufacturing.

By following EN 20273:1991 for clearance hole specifications, engineers and designers ensure reliable bolted connections, maintain interoperability across international standards, and optimize product performance in a wide range of industrial applications.