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Writer's pictureDIC Fasteners

An Introduction to the Bolt head types and Parts of Bolts

Updated: May 3, 2023

Bolts are an essential industrial fastener used to fasten and secure objects with the help of industrial nuts. Bolts are generally threaded fasteners that always use with industrial nuts. Their primary function is to attach aligned unthreaded holes by being placed through the aligned holes and secured with the bolt’s nut.

A bolt is mainly comprised of the following components:

Bolt Shaft: The shaft is a cylindrical portion that bears the shear forces acting on the bolt and secures the radial movements of the parts.

Parts of a Bolt:


  • Head: It is that portion of a bolt from where a spanner or wrench can hold it (to make it tight or loose).

  • Shank: The body of the bolt is the unthreaded part of a bolt placed under the head. Its length is measured from the head to the start of the transition to the threads. The shank provides a precise and smooth connection when installed in a bolt-hole. Pressure is more disrupted in this portion than in the threaded portion.

The fastener portion may produce or be exposed to vibration, increasing the chance of the bolt loosening. If a bolt has no shank (i.e., the bolt shaft entirely comprises of threading), the vibration may push back out of the fastened portions.

  • Thread: The thread is the continuous helical ridge made outside the bolt shaft. This part accommodates the nut and allows the bolt to be pushed in or out of the parts. The bolt’s thread mates with the internal threads of the industrial nut to create a bolted joint. All bolts must have a threaded portion, but most bolts have partially threaded shafts.

  • Grip length: It is the part of a bolt that accommodates the parts that are to be assembled. The grip length should be equal to the merged thickness of connected parts.

  • Nominal length: It is the sum of the grip length and the thread length.

Bolt Head Types:

The head of a bolt is responsible for bearing the axial torque, which holds the materials being fastened. A wrench or a driver holds and applies enough torque on the bolt head to tighten or loosen the bolt. Bolt's heads come in a wide variety of profiles and types; some of them are:

  • Hex bolt heads have a hexagonal, six-sided head that various tools can easily and quickly grip (e.g., wrenches).

  • Countersunk bolt heads have a conical profile with a flat/plain top. They generally have a recessed slot to allow screwdrivers or hex socket tools to apply torque and drive the bolt axially.

  • Dome-type bolt heads have a rounded and smooth profile. However, they are challenging to wrench externally.

DIC is an Exporter of all kinds of Standard and Custom Fasteners. For more info Contact us at: info@dicfasteners.com. The company has engaged a separate Quality Assurance team and qualified workforce to ensure standardized product delivery to the client.

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