ASTM A194 Hex Nut / 2HM Hex Nut.
ASTM A194 2H hex nut specification covers a variety of carbon, alloy, and martensitic and austenitic stainless steel nuts. These nuts are intended for high-pressure or high-temperature service, or both. Bars from which the nuts are made shall be hot-wrought. The material may be further processed by centerless grinding or by cold drawing. Austenitic stainless steel may be solution annealed or annealed and strain-hardened. Each alloy shall conform to the chemical composition requirements prescribed. Hardness tests, proof of load tests, and cone proof load tests shall be made to all nuts to meet the requirements specified. Unless otherwise specified, the American National Standard Heavy Hex Series (ANSI B 18.2.2) shall be used.
Nuts up to and including 1-inch nominal size shall be UNC Series Class 2B fit.
Nuts over 1-inch nominal size shall be either UNC Series Class 2B fit or 8 UN Series Class 2B fit.
High-strength ASTM A194 2H hex nuts are common in the marketplace and are often substituted for ASTM A563 grade DH nuts due to the limited availability of DH nuts in certain diameters and finishes.