Hex Head Bolt – a Basic Understanding

Hex bolts, also known as hexagonal head bolts, are threaded machine bolts used with a nut or in a tapped hole. As the name suggests, hex head bolts are hexagonal heads (6 sides) made from grade 2 galvanized steel, 316/304 stainless steel, and grade 5 zinc-plated steel

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Hex head bolts are designed to secure objects within or against other objects for a non-loosening hold. Applications for a hex bolt include fastening steel to steel, wood to wood, and other materials found on construction for projects such as highway structures, bridges, and buildings.

The Hex bolts allow for greater torque than traditional circular screws and tend to spin as you tighten and loosen them, making the need to hold with a wrench or socket. Hex bolts are commonly installed and removed with socket wrenches.

Hex head bolts come in two styles fully threaded and partially threaded. A fully threaded hex head bolt is used when it is matched up to a fully threaded hole. Partially threaded bolts are more rigid and have an unthreaded area under their head to allow for more holding strength when force is applied to the structure being secured.

Hex Head Bolts are not Hex Cap Screws 

Mistaking a hex cap screw for a hex bolt is very common, but the two fasteners differ in many ways, including how they are used and installed.

• Hex bolts are installed by turning a nut to tighten the fastener.

  
  

  Hex cap screws are installed into tapped holes by turning the head to assemble and tighten.

   

• Hex bolts have neither the washer face nor chamfered point.
  

  Hex cap screws feature a washer face on the bearing surface and the chamfered point.
  

• Hex bolts are often used in the construction industry, where mechanical properties are more critical than dimensional tolerances.

   

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  Hex cap screws are commonly used for precision applications where tight tolerance is required.

Hex Head Bolts Head & Thread Dimensions

Technical dimensional information for the head & threads of hex cap screws of all grades & materials. Technical dimensions include body diameter, width across the flats, width across the corners, head height & thread length.

The standard thread length of a hex head bolt:

Bolt lengths &#; 6&#;: Thread length = (2 X diameter) + 1/4&#;
Bolt lengths > 6&#;: Thread length = (2 X diameter) + 1/2&#;
Note: Most stock hex bolts 10&#; and longer will have 6&#; of thread.

The basic specs of a hex head bolt:

Diameters: 1/2 &#; 1&#;
Grade: ASTM A307 Grade A, F Grade 36
Lengths: 30&#; maximum
Finish: Plain and hot dip galvanized

Click For Tanners Complete Selection of Fasters and Bolts Including Hex Head Bolts and Hex Cap Screws 

The image above shows markings (radial lines) on the top of a hex head for grades 2, 5, 8 and L9. These markings are standard. For example, all grade 5 bolts will have three radial lines on the head. All grade 8 bolts will have six radial lines on the head. Watch the video below for more detail.

Grade 2 or Lower

If the cap screw has no markings on the head, it means it is made of low to medium carbon steel. These are the most inexpensive bolts on the market and intended for standard household use.

Grade 5

Hex heads with three markings are grade 5 fasteners. This grade is made from medium quality carbon steel. These are commonly used in automotive applications. Grade 5 cap screws are hardened. During manufacturing, they are heated in order to strengthen the outside of the screw. This makes the outside of the fastener stronger than the inside of the fastener.

Grade 8

With a tensile strength of 150,000 pounds per square inch, grade 8 hex cap screws are stronger than grade 5. This grade is heated similar to grade 5, but they are fully heat treated versus case hardened. Their strength makes them good candidates for tractor fabrication, suspension applications and other high demand fastening applications.

Grade L9

Grade L9 fasteners are made from high quality alloy steel. With a tensile strength of 180,000 pounds per square inch, L9 grade hex cap screws are perfect for high stress environments.

Metric Hex Cap Screws Grades

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