Hex Head Bolt – A Fundamental Insight

What is Hex Bolt?

Hex bolts, recognized as hexagonal head bolts, are threaded machine bolts utilized with a nut or in a tapped hole. Hex head bolts, with their six-sided design, are crafted from grade 2 galvanized steel, 316/304 stainless steel, and grade 5 zinc-plated steel.

These bolts are engineered for fastening materials within or against other materials to ensure a secure hold that resists loosening. Hex bolts are employed in various applications including the joining of steel to steel, wood to wood, and in the construction of infrastructure such as highways, bridges, and buildings.

Hex bolts enable greater torque application compared to traditional screws and exhibit rotation during tightening and loosening, requiring the use of a wrench or socket for manipulation. Socket wrenches are commonly used for the installation and removal of hex bolts.

There are two main types of hex head bolts: fully threaded and partially threaded. Fully threaded hex head bolts are suited for engagement with a fully threaded hole, whereas partially threaded bolts offer greater rigidity and feature an unthreaded section beneath the head for increased holding strength under load.

Finish & Grade Variations for Our Bolt Offerings

Our bolts from Gmetal are available in an array of finish and grade selections, each bringing distinct benefits such as resistance to corrosion and augmented strength.

Finishes & Treatments

  • Galvanized: Bolts that undergo a hot-dipped galvanization boast superior strength and resistance against corrosion. This process ensures a dense zinc coating on the fastener, enhancing its protection and longevity.
  • Plain: Bolts in their plain form bear no additional coatings or plating, save for an oil treatment to boost lubricity. The intrinsic corrosion resistance and strength are determined by the bolt’s material composition. Plain bolts are best suited for indoor usage or in settings where corrosion deterrents are not needed.
  • Zinc: The application of zinc plating bolsters corrosion resistance, strength, and lubricity for bolts. This zinc layer acts as a protective sacrificial barrier, corroding prior to the base material to extend the fastener’s lifespan.
  • 18-8 Stainless Steel: Known also as 304 stainless steel, bolts of 18-8 stainless steel composition deliver robust strength and commendable corrosion resistance. With 18% chromium and 8% nickel, these bolts find their place in a multitude of settings due to their adaptability.
  • 316 Stainless Steel: Distinguished by its inclusion of 2-3% molybdenum, 316 stainless steel bolts excel in resisting corrosion and pitting, maintaining their strength even under high temperatures.


  • Grade 2 bolts: Offering solid strength (57,000 psi), these bolts are typically crafted from low to medium carbon steel.
  • Grade 5 bolts: Presenting an enhanced strength level (74,000 psi), these are produced from medium carbon steel.
  • Grade 8 bolts: Boasting exceptional strength (130,000 psi), these are fabricated from medium carbon alloy steel.

Diverse Uses for Industrial-Grade Fasteners

Each type of bolt is crafted with distinct design features, suited to a variety of tasks.

Hex Head Bolt Uses

Widely utilized in a myriad of sectors, hex head bolts are a prevalent bolt type. They find use in:

  1. The automotive sector
  2. Construction field
  3. Home interiors and exteriors
  4. Manufacturing industry

A325 & A490 Structural Bolt Uses

Built for the rigors of construction tasks, structural bolts are robust fasteners. They’re often employed in:

  1. Erecting buildings
  2. Constructing bridges
  3. Highway development endeavors
  4. Joining steel frameworks

Carriage Bolt Uses

With a smooth, round head, carriage bolts are tailored for uses where a less intrusive bolt head is necessary, for both functional and visual purposes. Their usage spans:

  1. Timber constructions (such as walkways, lodges, storage buildings)
  2. The railway industry
  3. The mining sector
  4. Agricultural infrastructure

Lag Bolt Uses

Lag bolts are chosen for their strength in wooden construction projects, useful in:

  1. Joining wood pieces
  2. Attaching wood to metal
  3. Connecting wood to concrete or stone
  4. Supportive wood structures

Tension Control Bolt Uses

For applications demanding high tensile strength, tension control bolts are a go-to, suitable for:

  1. Steel framing projects
  2. Steel union constructions
  3. Bridge assemblies
  4. Building constructions

Hex Head Bolts vs. Hex Cap Screws

The confusion between hex cap screws and hex bolts is prevalent, yet they differ significantly in use and installation:

  • Hex bolts are fastened by tightening a nut.
  • Hex cap screws are fastened into tapped holes by turning the head.
  • Furthermore, hex bolts lack the washer face and chamfered point found on hex cap screws. Hex bolts are primarily used in construction settings where mechanical properties are prioritized over dimensional accuracy.

Hex cap screws are favored in precision applications where tight tolerances are critical.

Hex Head Bolts Head & Thread Dimensions

This section covers the technical dimensions for the head and threads of hex head bolts across all grades and materials. Specifications include body diameter, width across flats, width across corners, head height, and thread length.

Diagram Reference: Hex-Bolt-Diagram-1

The standard thread length for a hex head bolt is as follows:

For bolts ≤ 6″: Thread length = (2 X diameter) + 1/4″

For bolts > 6″: Thread length = (2 X diameter) + 1/2″


Key specifications for hex head bolts:

Diameters range from 1/2 to 1″

Grades include ASTM A307 Grade A, F1554 Grade 36

Maximum lengths up to 30″

Finishes include plain and hot-dip galvanized

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