Bolts: Compare Types, Materials & Features

Bolts are threaded fasteners used with compatible nuts or threaded components to create a secure, serviceable connection. The right choice depends on the joint design, the materials being joined, the available installation space, and the conditions the fastener will face.

This K-Catalog selection includes bolts from brands such as National Hardware, Bolt Dropper, Newlng, Mellewell, Hard-to-Find Fastener, MewuDecor, Fullerkreg, Chenango Supply, Orange Aluminum, KONGKI, Clipsandfasteners Inc, and Prime-Line. Compare each listing’s specifications carefully rather than choosing by appearance alone.

How to choose bolts

Start by identifying the connection and how the bolt will be installed. A conventional hex-head bolt may suit applications where a wrench can reach the head and nut. A carriage bolt can help provide a smooth, rounded exposed head, while specialty designs may be better for mounting, alignment, or hardware-specific jobs.

Consider these factors before selecting a product:

• Joint requirements: Determine whether the bolt must pass through prepared holes, fit a bracket, or work with a particular threaded component.
• Size and fit: Match the diameter, length, thread specification, and head clearance to the assembly.
• Material and finish: Choose materials and coatings appropriate for indoor use, outdoor exposure, moisture, corrosion concerns, or appearance.
• Installation method: Check whether the head shape allows the tools and access needed for tightening.
• Serviceability: For assemblies that may need maintenance, a removable bolt-and-nut connection can be more practical than a permanent fastening method.

Common bolt types

Bolt terminology can vary by application, manufacturer, and industry. Product listings should provide the details needed to confirm whether a particular style fits the job.

• Hex-head bolts: A common choice for general mechanical and construction assemblies where wrench access is available.
• Carriage bolts: Recognized by a rounded head and typically used where a less exposed head is preferred or where the bolt is installed through a square-sided opening.
• Flange bolts: Include an integrated flange beneath the head, which can distribute contact over a wider area than a conventional head.
• Shoulder bolts: Have a smooth shoulder section that can serve as a spacer, pivot, or locating surface in suitable assemblies.
• Eye bolts and U-bolts: Designed for attachment, hanging, bracing, or securing components when their specialized shape matches the application.
• Machine bolts: Often selected for equipment, hardware, and general assemblies that require a threaded fastener used with a nut.

For projects where a bolt is not the correct fastener, compare Screws and other options in the broader Fasteners category.

Specifications and features to compare

Thread details are among the most important specifications. Check the thread diameter, pitch or thread count, and threaded length. The mating nut or threaded part must use a compatible thread specification; similar-looking threads are not necessarily interchangeable.

Overall length also deserves attention. A bolt that is too short may not engage the nut adequately, while excessive length can interfere with surrounding parts. When measuring, verify how the manufacturer defines length for that particular head style.

Review the head dimensions and drive requirements as well. Head width, height, and shape affect wrench access, clearance, and how the bolt sits against the assembled material. If the product includes a finish or coating, consider whether it is intended for appearance, corrosion resistance, or both.

Material information can help with compatibility. Steel, stainless steel, aluminum, and other materials can differ in corrosion behavior, weight, strength characteristics, and suitability for the surrounding components. For structural, safety-critical, lifting, or high-temperature applications, follow the requirements of the equipment manufacturer or applicable professional standards instead of relying on general appearance.

Match bolts with nuts and washers

A bolt is usually selected as part of a complete fastening system. Compare Nuts to find a compatible mating component, and consider Washers when the joint design calls for load distribution, spacing, surface protection, or easier tightening.

Check that the nut style, thread specification, material, and finish are suitable for the bolt. Mixing incompatible materials or finishes may affect fit and long-term performance. Washers also need to match the bolt diameter and the surface or hole arrangement. In applications involving masonry or concrete, Anchors may be more appropriate than a conventional bolt passing through a predrilled hole.

Related fastening options

The best alternative depends on the materials, tools, and installation process. Collated Fasteners may be relevant for compatible powered fastening systems, while Nails can suit certain wood and construction tasks where a threaded connection is unnecessary. Compare the fastening method, removal requirements, and substrate before switching categories.

Frequently asked questions

What is the difference between a bolt and a screw?

A bolt is commonly used with a nut or a prepared threaded component, while a screw is generally driven into a material or threaded hole. Product terminology can vary, so check the listed design and intended use.

How do I select the correct bolt length?

Measure the materials and hardware being joined, then account for the nut, washer, and the amount of thread engagement required. Also confirm how the manufacturer measures length for the selected head style.

Do bolt threads need to match the nut exactly?

Yes. The diameter and thread specification must be compatible. A nut that appears to fit may still have the wrong pitch or thread form.

Should I use a washer with a bolt?

A washer may help distribute contact, protect a surface, provide spacing, or support the joint design. Whether it is appropriate depends on the assembly and the manufacturer’s instructions.

Which bolt material is suitable outdoors?

Choose a material and finish suited to the expected moisture, weather, corrosion, and contact conditions. For demanding environments, confirm the requirements with the equipment or project documentation.