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Originally approved in 1936, this specification is heavily utilized in petroleum and chemical construction applications.  The ASTM standard covers alloy steel and stainless steel bolting materials for high temperature service. This specification includes fasteners intended for use in pressure vessels, valves, flanges and fittings.

Although, this material is often available in national coarse (UNC) thread pitches, if being used in traditional applications, threads are specified 8 threads per inch (tpi) for diameters above one inch. Below is a basic summary of a few of the common grades. ASTM A193 covers a number of other standard specifications not covered in this description including B5, B6 and B16.

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The ASTM A194 specification covers carbon, alloy and stainless steel nuts intended for use in high-pressure and/or high-temperature service. 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 grade 2H 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.

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The ASTM A307 specification covers carbon steel bolts and studs ranging from 1/4” through 4” diameter. This is your everyday, run of the mill bolt specification often manufactured using A36 round bar. There are three grades A, B, and C* which denote tensile strength, configuration, and application. Refer to the mechanical properties chart for the subtle strength differences within each grade.

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Originally approved in 1948, the ASTM A320 specification covers alloy steel and stainless steel bolting materials for low temperature service. This standard covers rolled, forged, or strain hardened bars, bolts, screws, studs, and stud bolts used for pressure vessels, valves, flanges, and fittings.

Like the ASTM A193 specification, unless otherwise specified, the 8UN thread series is specified on fastener larger than 1” in diameter. Below is a basic summary of a few of the common grades within the ASTM A320 specification. A number of other less common grades of ASTM A320 exist, but not covered in the description below.

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The ASTM A325 specification covers high strength heavy hex structural bolts from ½” diameter through 1-1/2” diameter. These bolts are intended for use in structural connections and therefore have shorter thread lengths than standard hex bolts. Refer to the Structural Bolts page of our site for thread lengths and other related dimensions.

This specification is applicable to heavy hex structural bolts only. For bolts of other configurations and thread lengths with similar mechanical properties, see Specification A 449. Bolts for general applications, including anchor bolts, are covered by Specification A 449. Also refer to Specification A 449 for quenched and tempered steel bolts and studs with diameters greater than 1-1/2" but with similar mechanical properties.

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The ASTM A354 specification covers the chemical and mechanical requirements of quenched and tempered alloy steel bolts, studs, and other externally threaded fasteners 4" and under in diameter. Two strength levels, grade BC and grade BD, are summarized in the chart below. This specification is unrestricted in its configuration and can be a headed bolt, bent bolt, or threaded rod. Grade:


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ASTM A449 covers headed bolts, rods, and anchor bolts in diameters ranging from 1/4" through 3" inclusive. It is a medium strength bolt manufactured from a medium carbon or alloy steel that develops its mechanical values through a heat treating process. It is intended for general engineering applications.

ASTM A449 is virtually identical in chemistry and strength to ASTM A325 and SAE J429 grade 5. However, A449 is more flexible in the sense that it covers a larger diameter range and is not restricted by a specific configuration.

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The ASTM A490 specification covers quenched and tempered, alloy steel, heavy hex structural bolts from ½” diameter through 1½” diameter with a minimum 150 ksi tensile. These bolts are intended for use in structural connections and therefore have shorter thread lengths than standard hex bolts. Refer to the Structural Bolts page of our site for thread lengths and other related dimensions.

A490 bolts are similar in application and dimensions to A325 heavy hex structural bolts but are made from an alloy steel rather than a medium carbon steel, resulting in a higher strength fastener. The A490 specification is applicable to heavy hex structural bolts only. For bolts with different thread lengths than specified for structural bolts but with similar mechanical properties, see Specification A354 grade BD.

ASTM A490 bolts shall not be coated by hot-dip galvanizing, mechanical deposition, or electroplating with zinc or other metallic coatings due to the potential risk of hydrogen embrittlement. Additional testing in the form of Magnetic Particle Inspection for Longitudinal Discontinuities and Transverse Cracks is a requirement of the A490 specification.

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Recommended Nuts and Washers
Note: Nuts conforming to A194 Grade 2H are a suitable substitute for use with A490 heavy hex structural bolts. Follow the link for an ASTM A563 Nut Compatibility Chart. The bolts shall not be coated by hot-dip zinc coating, mechanical deposition, or electroplating with zinc or other metallic coatings due to the potential for hydrogen embitterment. Read more about issues with galvanizing ASTM A490. Each sample representative of the lot shall be magnetic particle inspected for longitudinal discontinuities and transverse cracks.

The ASTM A563 specification covers the chemical and mechanical requirements for carbon and alloy steel nuts used on bolts, studs, and externally threaded fasteners. The charts below address over tapping allowances for hot-dip galvanized nuts, grade marking requirements, and mechanical requirements. For information on suitable nuts for various grades of bolts, visit the Nut Compatibility Chart.

According the A563 specification, "The requirements for any grade of nut may, at the supplier's option, and with notice to the purchaser, be fulfilled by furnishing nuts of one of the stronger grades specified herein unless such a substitution is barred in the inquiry and purchase order". This is important because some nut grades are not readily available in certain sizes and finishes. Additionally, the specification allows for the substitution of ASTM A194 grade 2H nuts in lieu of A563 grade DH nuts due to the lack of availability of grade DH nuts in nominal sizes ¾" and larger.

Hot-dip galvanized nuts must be tapped oversize to allow for the added thickness of the zinc on the threads of the externally threaded fastener. These allowances are addressed in the chart below and a more detailed explanation of this issue can be found in the Frequently Asked Questions section of this site. Various nut styles exist and to some degree are determined by their grade. These styles include hex, heavy hex, square, jam, coupling and sleeve.

Scope:

• Standard specification for carbon and alloy steel nuts.

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The ASTM F1554 specification was introduced in 1994 and covers anchor bolts designed to anchor structural supports to concrete foundations. F1554 anchor bolts can take the form of either headed bolts, straight rods, or bent anchor bolts. The three grades 36, 55 and 105 designate the minimum yield strength (ksi) of the anchor bolt.

The bolts can be either cut or roll threaded and a weldable grade 55 can be substituted for grade 36 at the supplier’s option. Color coding on the end 36 blue, 55 yellow, and 105 red helps facilitate easy identification in the field. Permanent manufacturer and grade marking is allowed under the S2 supplementary requirements.

Applications for F1554 anchor bolts include columns in structural steel framed buildings, traffic signal and street lighting poles, and overhead highway sign structures to name just a few.

ASTM F2329 covers the requirements for hot-dip zinc coating applied to carbon steel and alloy steel bolts, screws, washers, nuts and special threaded fasteners applied by the hot-dip coating process.  This specification was developed in 2005, but is not yet widely used since many of the ASTM specification covering threaded fasteners do not reference it.  As soon as these specifications are updated to reference the ASTM F2329 specification, it will likely become much more prevalent than ASTM A153 which is the specification that is currently used to cover hot-dip galvanizing of bolts.  ASTM A123 is a related hot-dip galvanizing specification covering iron and steel products made from rolled pressed and forged shapes, castings, plates, bars and strips.