Heavy Hex Bolts

JIAXING SINI FASTENER CO., LTD. has manufactured bolts and screws since 2004, with production based in Haiyan, Zhejiang and Lianyungang, Jiangsu. We are a Heavy Hex Bolts manufacturer supplying quenched-and-tempered structural bolts in F3125 Grade A325 Type 1, ASTM A307 Grade B and A193 B7, dimensioned to ASME B18.2.1 heavy hex geometry and delivered with matching nuts and washers for steel-to-steel connections in buildings, bridges, industrial plants and towers.

What Our Heavy Hex Bolt Range Covers

A325 Type 1 Heavy Hex Bolts use a head that is larger across flats than a standard hex head, which spreads bearing load over a wider area of the connected plate and allows a hardened washer to be seated under the turned element. Our range is built around structural steel connections, equipment assembly and mechanical engineering projects where the joint carries sustained tension or shear.

• F3125 Grade A325 Type 1 — alloy steel, heat treated, for high-strength steel-to-steel structural connections.
• ASTM A307 Grade B — heavy hex general-purpose bolt for structural and equipment fastening at lower strength levels.
• ASTM A193 B7 — chrome-moly bolting for elevated-temperature and high-pressure flange and equipment joints.
• ASME B18.2.1 heavy hex — head and body dimensions held to the heavy hex series rather than the standard hex series.
• DIN 931 hex — metric partially threaded alternative where heavy hex geometry is not required by the drawing.
• Custom to drawing or sample — non-standard grip lengths, modified heads and OEM-specific configurations.

Specification Range at a Glance

Where Heavy Hex Bolts Fit

The heavy hex form is chosen when the connection is designed as a structural joint rather than a general assembly point. Typical positions include column-to-beam connections, bracing and splice plates, tower leg and cross-arm joints, machine bases, skid frames and heavy equipment anchorages.

• Steel structures — buildings, industrial plants, warehouses and towers where the bolt is tensioned to a specified minimum pretension.
• Bridge and infrastructure steelwork — girder splices and diaphragm connections exposed to weather, normally supplied with hot-dip galvanizing.
• Equipment and machinery assembly — bases, frames and mounting points where a wider bearing face under the head is preferred.
• Replacement and maintenance stock — the unmarked-head version suits positions where visual grade identification is not required.

Head Geometry, Thread Length and Joint Configuration

Two configuration decisions drive most heavy hex bolt specifications: how much of the shank is threaded, and how the head is marked. We produce both partially threaded and fully threaded versions so the unthreaded shank can sit in the shear plane, or so the bolt can accommodate a range of grip lengths on site.

Materials, Heat Treatment and Corrosion Protection

A325 Type 1 bolts are produced from alloy steel and heat treated to develop tensile and shear strength, then finished according to the exposure of the joint. A307 Grade B bolts are made from carbon steel for lower-strength general connections, while A193 B7 uses chrome-moly steel for elevated-temperature service. Most items in our programme are available in steel and stainless steel, in inch and metric sizes.

• Plain — for painted assemblies and controlled indoor environments.
• Black oxide — a thin, low-build finish used on B7 bolting and machined components.
• Zinc plating — the standard choice for indoor and sheltered outdoor steelwork.
• Hot-dip galvanizing — for bridges, towers and plant steelwork exposed to weather or humid process atmospheres.

Quality Control and Acceptance Testing

SINI FASTENER is ISO 9001 certified and inspects after each production process. Finished bolts are checked against the customer's requirements and the applicable international standard before packing. Our laboratory equipment includes an optical emission spectrometer for chemistry, a universal testing machine and tensile testing machine for mechanical properties, a hardness tester, a video measuring system for dimensional verification, a metallographic microscope and a salt spray test chamber for coating performance.

Acceptance documentation is prepared around the grade specified on the order — dimensional and thread gauging records, mechanical test results, coating checks and, where the project requires it, inspection certificates matched to the delivered lot.

Installation, Handling and Serviceability

Heavy hex structural bolts are installed with sockets sized to the heavy hex series and are normally tensioned by turn-of-nut, calibrated wrench or direct-tension-indicator methods, with a hardened washer under the turned element. The larger head face gives the wrench a stable grip and reduces the risk of rounding during high-torque tightening.

• Match the bolt grade with nuts and washers of the corresponding grade and finish so the assembly behaves as one system.
• Keep galvanized and plain bolts in separate site stores to avoid mixed assemblies in the same connection.
• Store in dry, covered conditions; coated threads should be protected until installation.
• Replacement bolts should repeat the original diameter, thread series, length and thread length to preserve the joint design.

Information We Use to Configure Your Solution

Our proposal is based on the working point, material and production target of the joint. The following inputs let us confirm grade, dimensions, finish and packing without back-and-forth.

• Grade and standard — F3125 A325 Type 1, A307B, A193 B7, DIN 931 or a customer specification.
• Diameter, thread series and thread class, in inch or metric.
• Length, thread length and whether the bolt is partially or fully threaded.
• Head marking requirement and any drawing or sample reference.
• Finish — plain, black oxide, zinc or hot-dip galvanized.
• Quantity, packing format, carton or pallet marking and delivery schedule.
• Documentation and inspection requirements for the delivered lot.

Related Fasteners From Our Range

Frequently Asked Questions

Which heavy hex bolt grades do you produce?

We produce F3125 Grade A325 Type 1, ASTM A307 Grade B and Carbon Steel Heavy Hex Bolts, together with DIN 931 hex bolts for metric projects. Items outside these grades are manufactured to customer drawings or samples.

What sizes and lengths are available?

Thread sizes run from 3/16" to 2" (M5 to M52) with lengths from 1/2" to 6" (12 mm to 600 mm) in the standard programme. Longer lengths and non-standard grip dimensions are produced to drawing.

Can the bolts be supplied hot-dip galvanized?

Yes. Plain, black oxide, zinc plated and hot-dip galvanized finishes are all available, and we match the nut and washer finish to the bolt so the assembly is consistent.

How is quality controlled before shipment?

Inspection takes place after each process, and finished bolts are checked against customer requirements and the applicable international standard. In-house testing covers chemistry, tensile and hardness, dimensional verification and salt spray performance.

Do you supply matching nuts and washers?

We supply heavy hex and standard nuts and washers in the matching grade, thread series and finish, so structural bolting assemblies arrive as a complete set rather than as separate items.

What do you need to prepare a quotation?

Send the grade and standard, diameter and thread series, length and thread length, finish, head marking requirement, quantity, packing format and any drawing or sample. With those details we confirm the configuration and the inspection scope for the lot.