Wecall Inc

Heavy hex nuts are specified for use with bolts or studs having any of the following characteristics: higher strength, zinc coatings or nominal thread size larger than 1-1/2".

Heavy hex nuts, as defined in ANSI B18.2.2 are greater in width and thickness than standard hex nuts. ASTM A563 is the most commonly referenced ASTM specification for carbon and alloy steel nuts. It includes 8 grades and covers sizes from 1/4" to 4".

ASTM A194 covers carbon and alloy steel nuts that are intended for use in high pressure and/or high temperature applications. It also covers sizes from 1/4" to 4" and includes dozens of grades. SAE J995 is another frequently referenced specification for carbon and alloy steel nuts. It covers sizes from 1/4" to 1-1/2" and includes three grades.

The geometry, dimensions and tolerances for Unified Inch screw threads are defined in ANSI B1.1. This specification includes information for UNC, UNF, UNEF and constant pitch (4UN, 6UN, 8UN etc.) threads.

Selecting the appropriate nut for an application is straightforward if the mating bolt or stud was produced to an ASTM standard. The heavy hex nut selection table is a summary of the ASTM recommendations.

Due to their wide availability in certain sizes, ASTM A194 Grades 2 and 2H nuts are frequently used in applications that are neither high pressure nor high temperature.

However, if there is some feature of the nut which makes it a 'special' or non-stock item, it is generally more economical to specify ASTM A563 Grades A or DH, unless the application actually involves high temperatures and/or pressures.

Likewise, the ASTM A563 grades are preferred over those of SAE J995 for small lot sizes and larger thread sizes. A563 Grades A, C and DH meet or exceed the strength requirements of J995 grades 2, 5 and 8, respectively.