Industrial Web Search Buyer's Guide Sector
Bolts, nuts, washers, anchor bolts, and threaded rod used to make load-bearing connections in steel structures, bridges, and equipment foundations. This sector covers the fasteners themselves plus the coatings, matched components, and documentation that determine whether a connection performs as designed.
Overview
A practical understanding of the sector is essential before comparing specific components: how fasteners are classified, what the grade on the drawing controls, and the types of companies you will engage with.
Structural fasteners are classified by the materials they connect. High-strength structural bolts, which join steel to steel, are governed by ASTM F3125. This standard consolidated six earlier standards in 2015 and designates A325 and A490 as grades within it, rather than as separate specifications. Anchor bolts are used to secure structural supports to concrete foundations and are covered by ASTM F1554, which has grades 36, 55, and 105 named after their minimum yield strength in ksi. General-purpose bolting, such as ASTM A307, is meant for lower-strength applications and should never be substituted for a specified structural grade.
In addition to grade, there are three other factors that come with every order: type, which differentiates standard steel from weathering steel; style, which distinguishes between heavy hex and twist-off tension control; and coating, which is determined by grade rather than being a freely chosen option. Do not source a structural bolt in isolation from its required nut, washer, coating, and installation method. The bolt, nut, and washer form a matched assembly, and specifying one component without the others often leads to ordering problems.
Three types of companies operate in this sector. Manufacturers produce the fasteners, and those that manufacture domestically can certify the domestic melt and production, which is important for federally funded projects. Distributors and master distributors stock standard sizes and grades from multiple manufacturers, making them the quickest option for common items, but they may not be suitable for anything long, bent, oversized, or nonstandard in configuration. Galvanizers and coating applicators handle the finishing process, sometimes as a separate step in the supply chain. This is crucial to understand, as coating is often where responsibility and traceability can become fragmented. It is easier to establish who is certifying what and who holds the documentation prior to placing an order than during an inspection.
Sourcing Considerations
The decisions below are the ones that most often cause regret later. The detail sits in the guides at the bottom of this page.
A structural fastener callout includes several key details: grade, type, style, coating, and often a standard for thread or dimensions. If you order based solely on grade, you leave four important characteristics for someone else to guess. Make sure to clarify any missing details from the drawing before placing your order, rather than addressing them after delivery.
Coating is not simply a matter of preference. Coating permissions are grade- and process-specific. Check ASTM F3125 and the governing project specification for the exact grade and coating system; do not assume that a corrosion-protection method allowed for A325 is allowed for A490. Additionally, a coating that is standard for one grade may be prohibited for another. It's important to verify the permitted coatings for your specific grade before deciding on a finish.
Structural specifications dictate how assemblies should be put together, not just the bolts themselves. The grade of the nut must match the grade of the bolt, and hardened washers are necessary where specified. Additionally, for galvanized assemblies, nuts must be tapped to accommodate the coating. Sourcing components from different suppliers can often lead to issues where parts do not fit together properly.
When working on federally funded projects, domestic sourcing may be required by contract rather than just preferred. Additionally, the standards for iron and steel products are stricter compared to those for final assembly in the United States. Before placing an order, confirm your project's specific requirements and verify the certifications your supplier can provide.
Pretensioned and slip-critical joints need a reliable installation method and pre-installation verification. The method you choose affects what you need to purchase, as you'll need to order tension-control bolts and direct-tension indicators rather than making adjustments on the spot. It's important to discuss this with the erector before finalizing the cost of the fastener package.
Standard diameters and lengths for common grades are available in stock. However, long anchor bolts, bent designs, oversized diameters, weathering steel, and items requiring galvanization are made to order. For these products, lead time is more critical than price for scheduling, and they are often identified late in the process.
Glossary
The terms you will meet on a drawing callout, a mill test report, or a fastener quote, in plain English.
A bolt or rod that anchors a structural support to a concrete foundation, supplied as a straight rod, a headed bolt, or a bent bolt. ASTM F1554 is the only ASTM specification written specifically for anchor bolts, and its three grades are 36, 55, and 105.
Structural bolting requirements apply to the complete bolt, nut, and washer assembly. Components must be compatible with the specified bolt grade, coating, and installation method; where preassembled or matched assemblies are specified, do not mix components.
A washer with raised protrusions on one face that flatten as the bolt is tightened. A feeler gauge measures the remaining gap to confirm the bolt reached its required pretension. Covered by ASTM F959 and used where installation must be independently verifiable.
A sourcing requirement stating that the steel was melted in the United States and that every subsequent manufacturing operation also occurred there. It is stricter than final assembly in the United States, and it is the standard that applies to iron and steel products on many federally funded projects.
The contact surface between two connected steel members where the clamping force acts. Its condition and coating determine the slip resistance of a slip-critical joint, which is why faying surface preparation is specified rather than assumed.
Raised or stamped identification on the bolt head showing the specification and grade. Head markings for A325 and A490 were retained when those specifications were consolidated into ASTM F3125, so field identification did not change. Absent, inconsistent, or unfamiliar markings should trigger a hold and review against the purchase order, certification package, and applicable specification before acceptance.
A heat-treated washer specified where an unhardened washer would embed into the connected steel and cause loss of pretension. ASTM F436 covers hardened washers. Substituting a general-purpose ASTM F844 washer where F436 is specified is a common and consequential ordering error.
A structural bolt with a head larger and thicker than a standard hex bolt, providing greater bearing area. Heavy hex is one of the two styles covered by ASTM F3125, alongside twist-off tension control.
The nut style specified for structural bolting assemblies, covered by ASTM A563 or ASTM A194. Nut grade must match bolt grade, and the correct grade depends on whether the assembly is coated.
A zinc coating applied by immersing the fastener in molten zinc, covered for fasteners by ASTM F2329. The most common coating for exposed exterior structural fasteners. It is not permitted in every grade, so availability varies by grade.
A delayed cracking failure in high-strength steel caused by hydrogen absorbed during acid cleaning or plating. ASTM F2329 identifies a risk for fasteners with a specified minimum product hardness of 33 HRC. This is the mechanism behind coating restrictions on the highest-strength grades, and the failure can occur after the structure is in service.
A zinc coating applied by tumbling fasteners with zinc powder and impact media rather than molten zinc or an electrolytic bath, covered by ASTM B695. It may be selected to reduce the risk of embrittlement in permitted applications, but buyers must still confirm that the process and coating class are permitted for the specified fastener grade.
The document certifying the chemical composition, mechanical test results, and heat number for the supplied material. It is the evidence trail that connects a fastener in a structure to the batch it came from, and it is what an inspector or auditor will ask for.
Enlarging the nut threads to accommodate the added thickness of a zinc coating on the bolt. Galvanized assemblies require it, which is why galvanized nuts are supplied specifically for galvanized bolts rather than taken from general stock.
A joint in which the bolt is deliberately tightened to a specified minimum tension, so the connection resists loosening under vibration and load reversal. Requires a verified installation method rather than ordinary tightening.
The tensile load a fastener must sustain without permanent deformation. Published per grade and used as an acceptance test value. Nut proof load must be compatible with the bolt it is used on, which is why nut and bolt grades are matched.
A joint that resists load through friction between the clamped surfaces rather than through the bolt bearing against the hole. Requires pretensioned bolts and a specified faying surface condition, and it is the most demanding of the three joint types to install and inspect.
The condition reached when the plies of a connection are brought into firm contact by the full effort of a worker with an ordinary wrench. It is the starting point for every pretensioning method and, for some joints, the final required condition.
The maximum tensile stress a fastener can carry before fracture, published in ksi or MPa. Together with yield strength it defines the grade, and it is the figure most often cited when comparing grades.
The tolerance class for the threads, such as Class 2A for external threads in the inch series. Governed by ASME B1.1. Class matters when threads are coated, when parts must assemble in the field, and when a specification calls out something other than the default.
A pretensioning method in which the nut is rotated a specified additional amount past snug-tight to achieve the required tension. One of several installation methods recognized by the RCSC Specification, each with its own pre-installation verification requirement.
A structural bolt with a splined end that shears off at a predetermined torque, providing visible confirmation that tension was reached. Covered as a style within ASTM F3125 and installed with a dedicated tool.
The two material types within ASTM F3125. Type 1 is medium carbon, carbon boron, or alloy steel. Type 3 is weathering steel, specified when the connected members are weathering steel so the fasteners corrode and patina at a similar rate.
Steel formulated to develop a stable protective oxide layer in exposed service, instead of requiring paint or other coatings. When structural members are weathering steel, fasteners should be Type 3 so the connection weathers consistently with the structure.
The stress at which a fastener begins to deform permanently, published in ksi or MPa. ASTM F1554 anchor bolt grades are named for their minimum yield strength, so Grade 105 means 105 ksi minimum yield.
A thinner zinc coating applied electrolytically, covered for fasteners by ASTM F1941. Suited to interior or controlled environments. It provides less corrosion protection than hot-dip or mechanical galvanizing and raises concerns about hydrogen embrittlement in higher-strength grades.
Standards
What each standard governs and why a buyer should care. Which ones apply depends on what you are connecting, the coating you need, and how the project is funded.
Bolt, nut, and washer specifications
Published by ASTM International, this specification outlines the requirements for high-strength structural bolts and assemblies. It was first issued in 2015 as a consolidation and replacement of six earlier standards: A325, A325M, A490, A490M, F1852, and F2280. A325 and A490 were withdrawn in 2016 and are now included as grades within F3125, with their head markings remaining unchanged to avoid disruption in field identification. The specification covers inch sizes from 1/2 inch to 1 1/2 inches and metric sizes from M12 to M36, in two types and two styles. Notably, a 144 ksi grade was added in the 2025 revision.
Published by ASTM International, this specification is the only one dedicated specifically to anchor bolts, including straight, headed, and bent configurations. It consists of three grades, 36, 55, and 105, named for their minimum yield strength in ksi (kilopounds per square inch). The specification also includes a color code applied to the projecting end of the bolts, allowing for easy identification of the grade in the field, even after the original markings have worn off.
Published by ASTM International, this document covers general-purpose carbon steel bolts and studs in Grades A and B. These are suitable for non-structural and lower-strength applications but should not be used as a substitute for specified high-strength structural grades.
Published by ASTM International, the specifications for nuts are specifically designed for use with structural bolting. It is essential that the nut grade matches the bolt grade. Additionally, the required nut grade changes when the assembly is galvanized. For this reason, nuts should be ordered based on the corresponding bolt rather than selected from general stock.
Published by ASTM International. Covers hardened steel washers for structural connections. Specified where an unhardened washer would embed into the connected steel and reduce pretension. Substituting general-purpose ASTM F844 washers where F436 is required is a recurring and consequential error.
Published by ASTM International. Covers compressible washer-type direct tension indicators, commonly called DTIs. Used to verify that a bolt reached its required pretension without relying on torque calibration, which makes them common where installation must be independently inspected.
Coatings and corrosion protection
Published by ASTM International. Governs hot-dip zinc coating applied to steel and alloy steel fasteners. It identifies a risk of internal hydrogen embrittlement for high-strength fasteners with a specified minimum product hardness of 33 HRC, which is the basis for coating restrictions on the strongest grades.
Published by ASTM International. Governs mechanically deposited zinc coatings. Because the process avoids the acid pickling and electrolytic steps associated with hydrogen uptake, it is specified where embrittlement is a concern on grades that permit it.
Published by ASTM International. Governs electrodeposited zinc coatings on threaded fasteners. A thinner coating suited to interior or controlled environments, offering less corrosion protection than hot-dip or mechanical galvanizing.
Design, installation, and procurement
Published by the Research Council on Structural Connections and referenced by the AISC Steel Construction Manual, this document defines three types of joints: snug-tightened, pretensioned, and slip-critical. It also outlines the recognized installation methods, which include turn-of-nut, calibrated wrench, twist-off tension control, direct tension indicator, and combined method. Each installation method has specific pre-installation verification requirements that must be met, particularly when the governing building code mandates them.
U.S. federal domestic sourcing requirements apply to federally funded infrastructure projects. For iron and steel products, all manufacturing processes, from initial melting to the application of coatings, must take place in the United States. Manufactured products are assessed based on the extent of domestic assembly and the domestic share of components' costs. Requirements, thresholds, and waivers vary by funding agency and program and are periodically updated. Therefore, it is important to confirm with the awarding agency which regulations apply to your specific project.
Published by ASME. The dimensional standard for unified inch screw threads. Structural bolts default to the coarse thread series unless otherwise specified, and thread class is drawn from this standard.
Published by ASME. The dimensional standard for heavy hex structural bolts and related components. Where F3125 governs material and strength, B18.2.6 governs physical dimensions, which is why both appear on a complete callout.
Frequently Asked Questions
Direct answers to the questions buyers ask most often when sourcing in this sector.
ASTM F3125 replaced several previous standards. It was first issued in 2015 as a consolidation of six structural bolting standards: A325, A325M, A490, A490M, F1852, and F2280. Both A325 and A490 were withdrawn in 2016 and are now included as grades within F3125. Therefore, a drawing that specifies A325 is effectively requesting F3125 Grade A325. The head markings on the bolts were intentionally left unchanged, so bolts in the field still bear the A325 or A490 markings, and their identification has not changed. Drawings issued prior to the consolidation remain valid and should be interpreted according to their original grade designations.
No. The ASTM F3125 standard explicitly states that both hot-dip galvanizing (per ASTM F2329) and mechanical galvanizing (per ASTM B695) are not permitted for Grade A490 bolts. This prohibition is due to the risk of hydrogen embrittlement in very high-strength steel, which can lead to delayed cracking once the structure is in service. For unpainted atmospheric exposure, Type 3 weathering steel may be appropriate where compatible with the connection and environment; otherwise, seek the engineer's approved corrosion-protection approach.
A snug-tightened joint is secured firmly between the connected layers using the full effort of a worker with a standard wrench; this represents the final condition of the joint. A pretensioned joint is tightened to the specified minimum bolt tension. Pretension may be required to meet the connection's structural design intent, including where slip resistance, fatigue performance, or resistance to separation is required. A slip-critical joint not only requires pretensioning but also depends on the friction between specially prepared surfaces to resist load, rather than relying solely on the bolt bearing against the hole. Each type of joint involves additional installation and inspection requirements, and the specific type of joint used is determined by the engineer rather than selected in the field.
The grade number of an anchor bolt indicates its minimum yield strength in kilopounds per square inch (ksi). Specifically, Grade 36 has a minimum yield strength of 36 ksi, Grade 55 has 55 ksi, and Grade 105 has 105 ksi. These grades pertain to anchor bolts that secure structural supports to concrete foundations and can be straight, headed, or bent. Additionally, each grade is assigned a color code for the projecting end of the bolt, allowing easy on-site identification, even after the original markings become obscured.
Hydrogen embrittlement is a delayed cracking failure that occurs in high-strength steel. It is caused by hydrogen absorbed during processes such as acid cleaning or electroplating, which becomes trapped in the material when it is under load. According to ASTM F2329, fasteners with a specified minimum hardness of 33 HRC are at risk. This is why the highest-strength grades have coating restrictions, while lower-strength grades can typically be galvanized without issues. The danger of hydrogen embrittlement lies in its potential to cause failure weeks or even months after installation, rather than during the component's initial use.
Not where a structural specification is called out. SAE J429 grades are automotive and general industrial specifications with different requirements for testing, marking, and supplied assemblies than those imposed by ASTM F3125 for structural connections. Structural bolting is governed by the assembly of bolt, nut, and washer together, and by the installation and inspection provisions of the RCSC Specification. If a drawing calls for a structural grade, substitution is an engineering decision, not a purchasing one.
It means the steel was melted in the United States and every subsequent manufacturing operation also took place there. It is a stricter requirement than final assembly in the United States. For federally funded infrastructure work, iron and steel products generally must meet this standard, with all manufacturing, from initial melting through the application of coatings, occurring domestically. Because coating counts as a manufacturing step, a domestically produced bolt galvanized abroad would not comply. Requirements vary by funding agency and program, so confirm what applies to your project.
Hot-dip galvanizing adds measurable thickness to a bolt's threads. To allow the nut to assemble, its internal threads are tapped oversize by a defined amount. This is why galvanized nuts are supplied specifically for galvanized bolts and should not be taken from general stock, and why nuts and bolts should be ordered together from the same source. An overtapped nut also has reduced thread engagement, which is accounted for in the specification through nut grade and strength requirements.
A direct tension indicator, or DTI, is a washer with raised protrusions that flatten as the bolt is tightened. A feeler gauge measures the remaining gap to confirm the bolt reached its required pretension. DTIs are covered by ASTM F959 and are one of several installation methods recognized by the RCSC Specification. They are commonly specified on bridges and high-profile structures where installation must be verifiable by a third party without relying on torque calibration. Because they are a purchased component, the decision affects the fastener order rather than just the erection method.
Buyer's Guides
In-depth guides covering the decisions above.
Buyer's Guide
Joint type, ASTM F3125 grade, the matched assembly, coating limits, installation method, and the traceability a critical connection has to document.
Read the guideMore coming
Additional guides are added when there is something genuinely worth saying, not on a schedule. IWS is committed to providing educational content to help you find the right suppliers!
Downloadable Resources
Practical tools you can take into a supplier conversation.
Checklist
Every detail a fastener supplier needs before they can quote accurately, in the order a callout is actually read. Bring it to the first conversation, and you will get comparable quotes instead of assumptions.
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