A325 Structural Bolt | Heavy Hex Marine Bolt | SINOFASTENER

ASTM A325 structural bolt — a high strength structural boltforship hull structural bolt connections in marine frame, bulkhead, and deck plate joints. Quenched and tempered carbon steel, heavy hex head, 1/2"–1-1/2"UNC. Now consolidated under ASTM F3125 Grade A325. Hot-dip galvanized, Dacromet, and plain finish. Matching A563 DH heavy hex nut and F436 hardened washer supplied as a complete connection system.

What Is ASTM A325 Structural Bolt?

ASTM A325 defines the requirements for a high strength structural bolt — a quenched and tempered carbon steel heavy hex bolt used in load-bearing structural steel connections. Type 1 (carbon steel) is the most widely specified grade, with minimum tensile strength of 120 ksi for sizes 1/2"–1"and 105 ksi for sizes 1-1/8"–1-1/2".

Since 2016, the original ASTM A325 standard has been consolidated into ASTM F3125/F3125M, which merges six legacy bolt standards (A325, A490, A449, F1852, F2280, F2280M) into a single specification. Products are now designated as ASTM F3125 Grade A325, though the term"A325"remains in universal use across the structural steel and marine fabrication industries.

TheASTM A325 structural bolt is used as a ship hull structural bolt for primary connections — transverse frame joints, watertight bulkhead flanges, deck plate splice connections, and hatch coaming assemblies. Unlike general-purpose hex bolts, every ASTM A325 heavy hex bolt undergoes mandatory heat treatment to achieve its specified tensile properties, verified by mill test certificates on every production batch.

Marine Applications

Note: The following applications are based on typical industry practice for ASTM A325 heavy hex structural bolts in marine structural connections per RCSC Specification.

Specifications & Materials

Why Choose sinofastener for High Strength Structural Bolts?

Standards Reference

• ASTM A325 — Standard Specification for Structural Bolts, Steel, Heat Treated, 120/105 ksi Minimum Tensile Strength (consolidated into F3125 in 2016)
• ASTM F3125/F3125M — Standard Specification for High Strength Structural Bolts and Assemblies (current superseding standard, A325 designated as Grade A325)
• ASTM A563 — Standard Specification for Carbon and Alloy Steel Nuts (Grade DH for structural applications)
• ASTM F436 — Standard Specification for Hardened Steel Washers
• ASME B18.2.1 — Square, Hex, Heavy Hex, 90 deg. Hex, Heavy Hex Flange, Socket, and Cable Bolts
• RCSC Specification for Structural Joints Using High-Strength Bolts (Research Council on Structural Connections)

FAQ

What is ASTM A325 structural bolt and what is it used for?

TheASTM A325 structural bolt is a quenched and tempered carbon steel heavy hex bolt with minimum 120 ksi tensile strength (sizes 1/2"–1") or 105 ksi (sizes 1-1/8"–1-1/2"). It is designed for load-bearing structural connections in ship hull framing, bulkhead assembly, and deck plate joints. As a ship hull structural bolt, it is specified in shipyard construction drawings per RCSC and classification society rules.

What is the difference between ASTM A325 and ASTM A490?

Both are high strength structural bolts, but with different material and strength grades. ASTM A325 (Type 1) is carbon steel with 120/105 ksi tensile; ASTM A490 is alloy steel with 150 ksi tensile across all sizes. A490 provides higher strength but is less ductile and not suitable for all connection geometries. For most ship hull structural bolt applications, A325 provides adequate strength with better ductility and fatigue performance.

What does ASTM F3125 Grade A325 mean?

ASTM F3125 Grade A325 is the current designation for products formerly specified as"ASTM A325". In 2016, ASTM consolidated six structural bolt standards — A325, A490, A449, F1852, F2280, and F2280M — into a single standard (F3125). The technical requirements for Grade A325 are identical to the original A325. Both designations refer to the same product; shipyards and fabricators may specify either"A325"or"F3125 Grade A325"interchangeably.

What nut and washer are required with ASTM A325 heavy hex bolt?

Per ASTM A325 and RCSC Specification, the ASTM A325 heavy hex bolt must be used with: (1) ASTM A563 Grade DH heavy hex nut — a high-strength nut matched to the bolt's proof load; and (2) ASTM F436 hardened steel washer — to distribute clamping force and prevent surface damage during torque installation. We supply complete bolt-nut-washer assemblies with matched heat lot traceability.