ASME · ANSI / ASME B18.2.1

ASME B18.2.1 Standard: Inch Fastener Specifications

ASME B18.2.1 Technical Standards: Fastener Specifications

This technical regulation establishes international requirements for the geometric parameters and dimensions of nine types of inch-series fasteners, including bolts and screws, certified as an American National Standard. Experts at EV Group China emphasize that these specifications are fundamental to ensuring the interchangeability and reliability of threaded connections in mechanical engineering.

The documentation includes manufacturing methods, marking rules, calculation formulas for determining dimensions, and product identification criteria. In disputed situations arising during product acceptance, the calculation formulas provided in the appendix to the standard take precedence. Please note that heavy hex structural bolts, previously classified under ASME B18.2.1, have been moved to the ASME B18.2.6 standard in the current edition.

The presence of a size in this standard does not guarantee its availability in the warehouse program; for clarification on supply nomenclature, we recommend sending inquiries to the EV Group China procurement department.

Comparability with ISO Standards

Since the ASME B18.2.1 standard is based on the imperial system of measurement, there are no direct equivalents in the ISO system. When designing assemblies requiring metric threads, appropriate international standards should be used.

Geometric Tolerances and Measurements

All linear dimensions are expressed in inches and refer to products without protective coatings. If an anti-corrosion layer is required, the final dimensions after processing must be pre-agreed between the contract parties. Decimal values are indicated without leading zeros before the decimal point and without non-significant zeros in the fourth decimal place. Geometric tolerances comply with the ASME Y14.5 standard.

Key Terminology

In the engineering practice of EV Group China, the following terms are used for the correct identification of fasteners:

  • Short bolt/screw: A product with a shank length requiring threading over the entire surface.
  • Long bolt/screw: A product with a combination of diameter and length where the thread is not cut over the entire length of the shank.
  • Body length (LB): The distance from the bearing plane of the head to the first thread or the beginning of the extrusion angle during rolling.
  • Grip length (LG): The maximum distance from the bearing surface of the head to the beginning of the threaded part, determined during manual assembly.
  • Thread length (LT): A reference dimension for calculation, measured from the edge of the product to the last full thread profile.