A193 Summary

a193ASTM A193 is a fastener specification covering alloy and stainless steel bolts and threaded studs for use with flanges, valves, pressure vessels, and fittings for high temperature and high pressure service.


B7 Bolt Head  b8  b8m  a193-b7m  a193-b16  a193-b5  a193-b6

Various grades exist within the A193 specification and vary in chemical composition, mechanical properties, and high temperature characteristics. The most common grade within the A193 specification is Grade B7, however several other grades exist.


stud bolt

Fasteners under the A193 specification are most commonly specified, manufactured, and supplied as heavy hex bolts or fully threaded studs. However, the specification does not restrict A193 fasteners to only these items.  A variety of bent bolts, rods with thread on one or both ends, and headed bolts other than heavy hex are commonly provided under the A193 specification. All bolts and studs shall be chamfered (pointed).



ASTM A962 is a related specification that covers a group of common requirements as they relate to the A193 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.


galv-b7Certain grades of fasteners manufactured to ASTM A193 can be zinc coated per F2329 (hot-dip galvanized), B695 (mechanically galvanized), or F1941 (zinc plated). Teflon, Xylan, and PTFE coatings in addition to cadmium plating are also commonly used with A193 bolts.

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 section 17 of the A193 specification, but rarely come into play.  Dual grade markings are allowed provided the fasteners meet all requirements of both specifications.


Unless otherwise specified, headed bolts shall be heavy hex with dimensions covered under ASME B18.2.1. Fully threaded studs under the A193 specification are typically measured from first thread to first thread, rather than the overall length which includes the chamfered ends.

Supplementary Requirements

Supplementary requirements of the A193 specification do not apply unless specified on the inquiry and purchase order. There are fourteen Supplementary requirements under the A193 specification that include special testing, processing, marking, and coating of fasteners.

Additional Resources


ASTM: This website provides a very brief overview of the A193 specification. If you are working with A193 heavy hex bolts and studs on a regular basis, we strongly recommend purchasing a copy of the ASTM A193 specification and ASTM A962 specification from ASTM international. ASTM International, formerly The American Society for Testing and Materials, is a standards organization covering a multitude of products including fasteners.

ASME: The American Society of Mechanical Engineers is an organization that develops dimensional standards for many fasteners including A193 heavy hex bolts. A copy of ASME B18.2.1 which covers heavy hex bolt dimensions and ASME B1.1 which provides dimensional criteria for both UNC and 8UN threads can be purchased from Techstreet.