The bolt fasteners are available in different designs to suit some specific purposes. A type of bolt with a special shape is a U-bolt. In this article, let’s understand the U-bolt with its structure, materials, types, installation steps, and size chart.
What Is a U Bolt?
The U-bolt is one of the bolt types, it refers to the fastener in the shape of letter U and have screw threads on both ends. U-bolts consist of a curved body with two straight, threaded arms extending downward, which allows the secure fastening of nuts and washers. The specific shape is used to clamp objects tightly, the clamping force can be distributed evenly while providing a robust support.
U Bolt Materials
U-bolts can be made from a variety of materials, common choices are carbon steel, stainless steel, and alloy steel. Carbon steel is a cost-effective and strong metal, it is great for making U-bolts that are used in non-corrosive environments like construction and automotive applications. Stainless steel is another popular material, often selected when excellent corrosion and heat resistance are needed, such as in marine, chemical, and food processing. Then, galvanized bolts are typically applied for outdoor and industrial fastening, and alloy steel bolts are optimal for heavy-duty applications and high-stress environments.
U-bolts can be coated with different materials, like zinc plating, for protection when used in some harsh environments.
Advantages of U-Bolts
- High clamping force and stable hold
- Various sizes and materials can be selected
- Numerous applications in construction, automotive, electrical, and more
- Great corrosion resistance with stainless steel material
- Easy to install and adjust, quick tightening and loosening
U Bolt Types
U-bolts primarily come in 3 different forms.
Round U Bolts
The most common type features a round bend and a relatively large curved selection. Round U-bolts are typically used to attach pipes or items to round objects in plumbing, electrical, and construction applications where cylindrical shapes are more common. This type is easier to manufacture than a square bend because of the simple design and bending process.
Square U Bolts
The distinctive feature is the square bend; square U bolts are designed to fit around square or rectangular objects for structural support or automotive applications. The bends must have a radius that is at least twice the diameter of the material being bent, in order to avoid compromising the integrity of the U-bolt during manufacturing.
Semi-round U Bolts
Another type is called semi-round U bolts, which are a type of U-bolt that combines the features of round and square bend U-bolts. There is a slightly arched bottom with a flatter section. The shape combines the flexibility of round U-bolts and the stability of square U-bolts, and can adapt to objects of different shapes.
U Bolt Installation – How to Install U-Bolts?
To ensure the proper installation of U-bolts on pipes, the first step is to prepare the required tools, including nuts, washers, a measuring tape, a wrench or socket set, a torque wrench, and an anti-seize lubricant (optional).
- Measure and mark: Determine the exact installation position of the U-bolt to ensure it meets the application requirements. Use a marker pen or chalk to mark the position of the hole for inserting the U-bolt.
- Drill holes: If drilling is required, please choose a drill bit that matches the diameter of the U-bolt. The diameter of the hole should be slightly larger than the diameter of the U-bolt for easy insertion. Carefully drill the marked holes, ensuring they are straight and clean. Remove any debris or burrs from the hole.
- Put in the U-bolt: insert the bolt around the object to be held or put it through the holes, make sure the alignment is correct, and it levels with the surface. Place the washer on the threaded end of the U-bolt, and then place the nut.
- Tighten the nuts: Use a wrench or socket set to tighten the nuts evenly. Use two nuts alternately to ensure uniform pressure and alignment. Then, use a torque wrench to apply the recommended torque to the size and material of the U-bolt. Appropriate torque can ensure safe and reliable installation. Check the manufacturer’s specifications to understand the correct torque values.
- Check alignment and tightness: Check if the U-bolts are aligned correctly and if the fixed object is firmly secured in place. There should be no gaps or movements. After the initial installation, recheck the tightness of the nut. Re-tightening the nut after a short period of use is also a good practice to consider any settlement.
U Bolt Dimensions – U Bolt Size Chart
The critical dimensions of U-bolts include their length, diameter, and width. Below is a dimension chart of U-bolts according to the standard DIN 3570.
| Dimensions | 23 | 30 | 38 | 46 | 52 | 64 | 82 | 94 | 120 | 148 | 176 | 228 | 282 | 332 | 530 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| pipe nominal width | 15 | 20 | 25 | 32 | 40 | 50 | 65 | 80 | 100 | 125 | 150 | 200 | 250 | 300 | 500 |
| D₁ | 20 to 21 | 25 to 26.9 | 30 to 33.7 | 38 to 42.4 | 44.5 to 48.3 | 57 to 60.3 | 76.1 | 88.9 | 108 to 114.3 | 133 to 139.7 | 159 to 168.3 | 216 to 219.1 | 267 to 273 | 318 to 323.9 | 508 to 521 |
| B | 30 | 40 | 40 | 50 | 50 | 50 | 50 | 50 | 60 | 60 | 60 | 70 | 70 | 70 | 70 |
| D₂ | 10 | 10 | 10 | 10 | 10 | 12 | 12 | 12 | 16 | 16 | 16 | 20 | 20 | 20 | 24 |
| D₃ | M10 | M10 | M10 | M10 | M10 | M12 | M12 | M12 | M16 | M 16 | M16 | M20 | M20 | M20 | M24 |
| E | 33 | 40 | 48 | 56 | 62 | 76 | 94 | 106 | 136 | 164 | 192 | 248 | 302 | 352 | 554 |
| H | 60 | 70 | 76 | 86 | 92 | 109 | 125 | 138 | 171 | 191 | 217 | 283 | 334 | 385 | 589 |
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