Hex bolts are among the most familiar mechanical fasteners because the external hex head is easy to grip with a spanner or socket. They are used in machinery, brackets, frames, equipment and many general assemblies. A good hex-bolt specification includes thread size, length, pitch, material, property class or stainless grade, thread coverage and finish.
Buying only by length and diameter can create problems when the head size, pitch, strength or material does not match the joint. In maintenance work, it is especially important to identify whether the original bolt is a standard coarse metric thread and whether the replacement needs the same mechanical property class.
Quick answer: Hex bolts are among the most familiar mechanical fasteners because the external hex head is easy to grip with a spanner or socket.
What to know about hex bolts guide
External hex head
The head is driven from the outside, making hex bolts convenient when there is enough radial tool clearance for a socket or spanner.
Thread and length
Metric hex bolts use an M-size and defined pitch. Length is typically measured from under the head to the end of the fastener.
Material and property
Stainless-steel bolts are selected for corrosion resistance; carbon or alloy steel bolts are commonly selected by property class where higher mechanical strength is required.
Washer and nut pairing
The nut must match diameter and pitch. A plain washer may be used to spread bearing load, protect the surface or provide a consistent bearing face.
How to choose the right fastener
- Check the required strength: Do not replace a marked high-strength bolt with an ungraded fastener simply because it fits.
- Match the material to the environment: SS304 suits many general applications; harsher chloride exposure may need a more corrosion-resistant material.
- Confirm grip length: Ensure the unthreaded and threaded portions, if applicable, suit the clamped stack.
- Allow tool clearance: Hex heads require space around the head for the socket or spanner.
- Pair with suitable nut and washer: Match thread and material and review locking needs.
Quick comparison
| Specification item | Example | Why it matters |
|---|---|---|
| Thread | M6×1.0 | Must match nut/tapped hole |
| Length | 20 mm | Controls clamp stack and engagement |
| Material | SS304 | Corrosion and environment |
| Finish | Natural stainless | Surface condition/appearance |
| Nut | M6 matching pitch | Creates compatible thread pair |
A practical ordering workflow
Before placing an order for hex bolts guide, turn the application into a short specification. Start with the mating thread and physical envelope, then confirm the head or drive, material and finish. If the fastener is part of a loaded, vibrating, outdoor or frequently serviced joint, add the relevant mechanical, corrosion and maintenance requirements before choosing a SKU.
For repeat purchases, record the exact approved description in your bill of materials or purchasing system instead of relying on a photograph or an old sample. That record should include the dimensions that control fit, the material or property class, the finish, and any standard or certificate requirement. This makes replacement orders easier to compare and helps prevent accidental substitutions.
When a dimension, torque value, strength requirement or corrosion condition is safety-critical, use the applicable engineering drawing, current standard and manufacturer documentation as the final authority. Catalogue guidance is useful for narrowing choices, but it should not override the requirements of the actual joint.
How to verify the specification before ordering
Make the first verification on the actual assembly or approved drawing. For check the required strength, do not replace a marked high-strength bolt with an ungraded fastener simply because it fits. For match the material to the environment, sS304 suits many general applications; harsher chloride exposure may need a more corrosion-resistant material. Do not assume that an older fastener removed from the machine is still the approved specification; previous repairs may have introduced substitutions.
If the part is being introduced into production, buy a small validation quantity before committing to a large lot. Check thread engagement by hand, seating of the head or nut, tool clearance, surface marking, interference with nearby parts and the condition of the mating thread after assembly. Where traceability or mechanical properties matter, compare received markings and documents with the purchase specification. This small verification step is especially useful when changing suppliers, materials, finishes or dimensional standards.
Common mistakes to avoid
- Using a lower-strength replacement in a loaded assembly.
- Choosing a bolt that bottoms out before clamping the joint.
- Using a nut with the wrong pitch.
- Assuming stainless grade alone tells you the bolt's complete mechanical properties.
- Using an external hex head where there is no room for a socket.
Recommended products and categories
You can continue from this guide by viewing shop hex bolts, M6×20 SS304 hex bolt and matching plain washers.
Technical references
The following independent technical references are useful for checking terminology, standards and engineering background. They are provided for reference and do not imply endorsement of any product sold on this site.
Frequently asked questions
How is a hex bolt length measured?
Typically from the underside of the hex head to the end of the bolt.
Do all M6 bolts use 1.0 mm pitch?
1.0 mm is the common coarse pitch, but fine-pitch M6 threads also exist. Verify the mating thread.
Should I use a washer with a hex bolt?
A washer is useful when load distribution, surface protection or a controlled bearing face is needed.
Can an SS304 hex bolt replace a high-tensile steel bolt?
Not automatically. Material and strength class are separate requirements, so check the design specification.
Related reading
Final buying checklist
- Confirm the nominal thread diameter and thread pitch.
- Confirm the required length and the correct head-to-tip measuring method.
- Check head style, drive style and installation-tool access.
- Match material and finish to the service environment and mating materials.
- Check strength, locking, documentation and application limits where they matter.
A hex bolt is simple to use, but the specification must still control thread, length, material and mechanical performance. Match the complete bolt to the joint rather than selecting only from the visible dimensions.
Ready to select a part? Browse our Screws, Nuts & Bolts catalogue and filter by thread size, material, finish, head style and drive type.