A hex bolt is a bolt with a six-sided head, used together with a nut and washer to join two or more components in structures, machinery, and industrial installations. The design is simple, but the strength grade, thread type, and material you choose have a major impact on how safe the connection is.
This guide covers the types of hex bolts, how to read strength grades, material and finish options, and how to choose the right one for your project.
What Is a Hex Bolt?
A hex bolt has three main parts: a hexagonal head, a shank, and a threaded section. The six-sided head can be tightened with a wrench or socket from multiple angles and can handle high torque. Hex bolts are normally paired with a hex nut and washer to create a strong connection that can be disassembled when needed.
Where Hex Bolts Are Used in Construction and Industry
Hex bolts are among the most widely used fasteners because they suit so many applications:
- Steel structure connections in buildings, bridges, and towers
- Mounting machinery, frames, and industrial equipment
- Connections on platforms, racks, and supporting structures
- Component assembly in manufacturing and automotive industries
Types of Hex Bolts
Partially Threaded Hex Bolt
Only part of the shank is threaded, and the section near the head is left plain. This unthreaded portion resists shear loads better, so this type is widely used in structural connections. Dimensions follow ISO 4014 or DIN 931.
Fully Threaded Hex Bolt
The thread runs almost the full length of the shank, up to the underside of the head. It suits thin materials or applications that need more thread length for adjustment. Dimensions follow ISO 4017 or DIN 933.
Heavy Hex Bolt
This type has a wider, thicker head and is designed for high-strength structural steel connections. It is used with matching heavy hex nuts and washers.
Understanding Hex Bolt Strength Grades
On metric hex bolts, the number marked on the head is the property class defined in ISO 898-1. The first number multiplied by 100 gives the nominal tensile strength in MPa. The second number multiplied by 10 gives the ratio of yield strength to tensile strength as a percentage.
For example, grade 8.8 has a nominal tensile strength of 800 MPa and a yield strength of about 80% of that, which is 640 MPa.
| Grade | Tensile Strength (nominal) | Yield Strength (nominal) | Typical Use |
| 4.8 | 400 MPa | 320 MPa | Light loads, non-critical applications |
| 8.8 | 800 MPa | 640 MPa | General construction and machinery |
| 10.9 | 1,000 MPa | 900 MPa | Structures and machinery under heavy loads |
| 12.9 | 1,200 MPa | 1,080 MPa | Specialized applications with very high loads |
Hex Bolt Materials and Finishes
Materials
- Carbon steel: the most common choice for grades 4.8 and 8.8
- Alloy steel (heat treated): used for grades 10.9 and 12.9
- Stainless steel: SS304 (A2) for general environments, SS316 (A4) for coastal areas and chemical environments
Finishes for carbon and alloy steel
- Electro plating: basic protection for indoor use
- Hot-dip galvanizing: a thick zinc layer for outdoor and humid environments
- Fluoro carbon coating: added protection for aggressive environments
For grade 10.9 and above, the finishing method needs to be chosen carefully because of the risk of hydrogen embrittlement. Consult the manufacturer before deciding on a coating.
How to Choose the Right Hex Bolt
1. Determine the Required Load and Grade
Calculate the tensile and shear loads the bolt will carry, then choose a grade with capacity above the actual requirement.
2. Choose the Thread Type
Use a partially threaded bolt for connections that resist shear, and a fully threaded bolt for thin materials or when adjustment is needed.
3. Match the Material and Finish to the Environment
Galvanized carbon steel suits general conditions, while stainless steel suits corrosive environments.
4. Check the Size and Length
Make sure the diameter and thread pitch match, and that the bolt is long enough for two to three threads to extend past the nut once it is fitted.
5. Pair It with a Nut and Washer of the Matching Grade
Use a nut with a compatible strength class, for example a class 8 nut with a grade 8.8 bolt, and a class 10 nut with a grade 10.9 bolt.
6. Confirm Material Certification
Ask the supplier for COO and COC documents to make sure the material is traceable.
Hex Bolt Standards and Certification
- ISO 898-1: property classes for carbon and alloy steel bolts
- ISO 4014 and ISO 4017: dimensions for partially and fully threaded hex bolts, equivalent to DIN 931 and DIN 933, which are still widely used as references
- ISO 3506: specification for stainless steel fasteners
- ASME B18.2.1: dimensions for inch-size hex bolts
- ASTM A307 and ASTM F3125: specifications for steel bolts in general-purpose and structural applications
Quality hex bolts should come with a Certificate of Origin (COO) and a Certificate of Conformity (COC) as proof of material traceability.
Hex Bolts from Karunia Utama
Karunia Utama has been a fastener manufacturer since 2015, producing hex bolts to ASTM, DIN, ASME, ISO, and JIS standards, backed by COO and COC certification. Carbon steel and stainless steel options are available, with electro plating, hot-dip galvanizing, and fluoro carbon coating finishes.
To complete your connection, we also supply Hex Nuts and Flat Washers, along with Anchor Bolts, Stud Bolts, Eye Bolts, U-Bolts, TC-Bolts, Span Screws, Turnbuckles, clamp bolts, clamp gratings, and wire mesh. For custom sizes or non-standard specifications, our team is ready to help design a suitable solution.
Conclusion
The right hex bolt comes down to three things: a strength grade that matches the load, a thread type that suits the connection, and a material and finish that fit the environment. Always pair the bolt with a nut and washer of the matching grade, and choose a manufacturer that provides valid material certification.
Ready to start your project? Send your hex bolt specifications to the Karunia Utama team at +62 857-7228-2180 or cs.karuniautama@gmail.com, and get a quote tailored to your project requirements.