Bolt Tightening Torques
Bolts play a critical role in joining two parts together firmly and securely. However, correct joining is not only achieved with the type of bolt, but also with the correct tightening torque. Torque value is the most important factor that determines how much force a bolt should be tightened.
Torque means turning force and is measured in Nm (Newton meters). Tightening a bolt too little will cause the connection to remain loose and prevent a strong connection. Tightening too much will damage and deform both the bolt and the parts connected.
So how is torque value determined?
Bolt tightening torque is determined by the following factors
• Bolt diameter and thread structure
• Material type (e.g. stainless steel, carbon steel)
• Strength class (e.g. 8.8, 10.9)
• Surface coating (galvanized, black oxide, etc.)
• Whether the fasteners are lubricated
There are standard torque values determined by manufacturers for each bolt type and these values must be followed. If you ask why the correct torque value should be applied;
• Overtightening can cause the bolt to stretch, break or strip the thread.
• Insufficient tightening causes the connection to loosen over time, causing play or vibration in the parts.
• Especially in the automotive, machinery and construction sectors, assembly with the correct torque is of vital importance.
How to Calculate Bolt Tightening Torque?
A correct bolt torque tightening calculation directly affects both the safety of the connection and the life of the product. Determining the appropriate torque value should be done according to the type of material used, surface coating and connection conditions. For companies that manufacture bolts, this information is important for both product development and customer information. The bolt tightening torque calculation can generally be calculated with the following formula:
Torque (Nm)=K×F×d\text{Torque (Nm)} = K \times F \times dTorque (Nm)=K×F×d
Where
• K = Coefficient of friction (approximately 0.18–0.25; varies depending on surface condition, lubrication and coating)
• F = Axial tightening force (N)
• d = Nominal diameter of the bolt (m)
Example:
For a bolt with a diameter of M10 that needs to be tightened with an axial force of 40,000 N,
if K = 0.2 is taken:
\text{Torque} = 0.2 \times 40,000 \times 0.01 = 80 , \text{Nm}
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Things to Consider in Torque Calculation
• Is it oiled or dry?
Since friction is reduced in lubricated connections, lower torque is sufficient. Therefore, different K coefficients are used for lubricated connections.
• Bolt class and quality:
Bolts with strength classes such as 8.8, 10.9 can withstand different forces. This also affects the torque calculation.
• Use of torque tables:
Torque tables prepared by manufacturers, especially for standard bolts, allow you to make practical and safe calculations.
How is Torque Applied?
The desired force is applied to the bolt using torque wrenches. Digital and manual torque wrenches are the basic tools preferred in precision applications.
Torque value in bolted connections is not just a technical detail, but an indispensable criterion for the safety and long-term use of the connection. Correct torque application in production and assembly both increases work safety and minimizes part damage.
Bolt Tightening Torque Values Table
Bolt Diameter Strength Class Recommended Torque (Nm)
M8 8.8 25 – 30 Nm
M10 10.9 50 – 55 Nm
M12 10.9 90 – 100 Nm
M16 10.9 210 – 220 Nm
These values are general recommendations for non-lubricated connections. The torque value may be lower in lubricated connections. It is always necessary to act according to product specifications.
Torque-Resistant Bolts and Our Products
High-strength bolts produced by our company can be used safely in difficult applications. Especially:
• 8.8 – 10.9 quality bolts
• Galvanized coated anti-rust screws
• Special production bolts suitable for automotive and heavy industry
All our products are produced in accordance with quality standards and are subjected to torque strength tests. You can contact us via the Acar vida communication channel to examine our products and get detailed information.
Frequently Asked Questions (FAQ)
1. Why is bolt torque important?
Tightening the bolt with the correct torque ensures that the connection is safe and long-lasting. Insufficient or excessive torque can cause part damage.
2. How to tighten a bolt without a torque wrench?
Using a torque wrench is the most accurate method. However, alternative tightening methods determined by the torque table and hand strength can be used, but they are not precise.
3. Is the same torque value applied to each bolt?
No. The torque value varies according to factors such as the diameter, strength class, material and coating type of the bolt.
4. Is there a difference in torque for lubricated bolts?
Yes. Since friction is reduced in lubricated bolts, the same tightening force can be achieved with lower torque. Therefore, less torque is applied than standard torque in lubricated connections.
