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Galvanized & Blackened Double-Headed Bolts 4.8/8.8 Grade - China Suppliers & Factory Quality Products
| Thread size d |
M6 | M8 | M10 | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M33 | |
| designation① | D | D | D | D | D | D | D | D | D | D | D | D | D | |
| / | / | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | D-HDZ | ||
| ds | Max | 5.32 | 7.16 | 8.99 | 10.83 | 12.66 | 14.66 | 16.33 | 18.33 | 20.33 | 22 | 25 | 27.67 | 30.67 |
| Min | 5.14 | 6.97 | 8.78 | 10.59 | 12.41 | 14.41 | 16.07 | 18.07 | 20.07 | 21.69 | 24.69 | 27.34 | 30.34 | |
| S | Public | 50 | 63 | 75 | 100 | 115 | 125 | 140 | 150 | 165 | 175 | 200 | 200 | 225 |
| Max | 75 | 88 | 100 | 125 | 140 | 150 | 165 | 175 | 190 | 200 | 225 | 225 | 250 | |
| Min | 42 | 55 | 67 | 92 | 107 | 117 | 132 | 142 | 157 | 167 | 192 | 192 | 217 | |
| Connecting nut | M6 | M8 | M10 | M12 | M14 | M16 | M18 | M20 | M22 | M24 | M27 | M30 | M33 | |
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The Function of Double Headed Bolts
1
Connecting Mechanical Components
Double headed bolts have threads at both ends and a screw in the middle, commonly used to connect mechanical components such as mining machinery, bridges, automobiles, motorcycles, boiler steel structures, suspension towers, large-span steel structures, and large buildings.
2
Installation Accessories
When large equipment requires the installation of accessories, such as observation mirrors, mechanical seal seats, reduction frames, etc., double headed bolts can play a role. One end is screwed into the main body, and after installing the accessories, the other end is equipped with a nut. Due to the fact that these attachments may require frequent disassembly, using double headed bolts for replacement would be very convenient.
3
Connecting Thick Plates and Places Where It Is Inconvenient to Use Hexagonal Bolts
In cases where the thickness of the connectors is large or the connection area is not convenient to use hexagonal bolts, such as concrete roof trusses, roof beam suspensions, monorail beam suspensions, etc., double headed bolts are also a suitable choice.
4
Fixed Connecting Rod
Double headed bolts are also commonly used for mechanical fixed connecting rods, with corresponding threads at both ends. The thickness of the middle screw varies depending on actual usage.
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Frequently Asked Questions
What is a double headed bolt and how does it differ from a standard bolt?
A double headed bolt (also called a stud bolt) features threads at both ends with an unthreaded shank in the middle. Unlike a standard bolt that has a fixed head, both ends of a double headed bolt can be threaded into components or fitted with nuts, making it ideal for connections that require easy disassembly without disturbing the embedded end.
What does the "D-HDZ" designation mean in the specification table?
"D-HDZ" refers to a double headed bolt with a hot-dip galvanized (HDZ) surface coating. This treatment provides superior corrosion resistance compared to standard finishes and is available for thread sizes M10 and above, making it especially suited for outdoor, marine, or high-humidity environments.
What thread sizes are available for double headed bolts?
Double headed bolts are available in metric thread sizes from M6 through M33, covering M6, M8, M10, M12, M14, M16, M18, M20, M22, M24, M27, M30, and M33. Each size has defined Min and Max values for the shank diameter (ds) and screw length (S), as listed in the specification table above.
In which industries are double headed bolts most commonly used?
Double headed bolts are widely applied across heavy industries including mining machinery, bridge and civil construction, automotive and motorcycle manufacturing, boiler and pressure vessel fabrication, suspension towers, and large-span steel structures. They are also used in concrete roof trusses, roof beam suspensions, and monorail beam systems.
Why are double headed bolts preferred for equipment accessories that require frequent removal?
Because one end of the bolt remains permanently threaded into the main body, only the nut on the other end needs to be loosened during disassembly. This eliminates wear to the threaded hole in the main component and makes repeated removal and reinstallation of accessories — such as observation mirrors or mechanical seal seats — significantly faster and more reliable.
How do I select the correct double headed bolt size for my application?
Selection should be based on the required thread diameter (d), shank diameter (ds), and total screw length (S). Use the Min and Max tolerance values in the specification table to verify compatibility with your components. For structural or load-bearing applications, it is recommended to consult a qualified mechanical or structural engineer to confirm the appropriate grade and size.