A320 Summary

ASTM A320 is a fastener specification covering alloy and stainless steel bolts and threaded studs for use with flanges, valves, pressure vessels, and fittings for low-temperature service.


There are several grades within the A320 specification. Choosing the correct grade depends on several factors, such as mechanical properties, low-temperature characteristics, and service conditions.


A320 fasteners can be specified as heavy hex bolts, fully threaded studs, bent bolts, other headed bolts and rods with threads on each end or one end. Bolts and studs manufactured to the A320 specification require chamfered ends. The most common configurations for A320 fasteners are heavy hex bolts and fully threaded studs.


ASTM A962 is a related specification that covers a group of common requirements as they relate to the A320 specification.  Section 13 of the A962 specification addresses thread form and class. Threads shall comply with ASME B1.1, Class 2A and can be cut or rolled. For diameters 1” and smaller, Unified National Coarse (UNC) thread series is used, and for diameters larger than 1”, eight-pitch thread series (8UN) shall be used, unless otherwise specified.


All grades of A320 bolts require mechanical tests that include yield, tensile, elongation, and reduction of area. Certain grades within the A320 specification may also require an impact test.


Certain grades of A320 fasteners can be zinc coated per F2329 (hot-dip galvanized), B695 (mechanically galvanized), or F1941 (zinc plated). Cadmium plating in addition to other coatings can performed on some grades as well.

Product Marking

Both the grade symbol and manufacturer’s identification are applied to the heads of bolts and one end of studs. Allowance for the omission of product marking on very small diameter fasteners and makings in alternate locations are laid out in the A962 specification, but rarely come into play.  Dual grade markings are allowed provided the fasteners meet all requirements of both specifications. This is covered in ASTM A962 (section 20).


Unless otherwise specified, headed bolts shall be heavy hex screw series with dimensions covered under ASME B18.2.1. Typically, fully threaded studs under the A320 specification are measured from first thread to first thread, rather than the overall length which includes the chamfered ends.

Supplemental Requirements

Supplementary requirements of the A320 specification shall not apply unless specified in the inquiry and purchase order. There are three Supplementary requirements under the A320 specification that include impact properties, lateral expansion and hardness testing for class 2 bolting materials.