Thread Rolling and Blank Diameter
Thread rolling is a process of forming threads by cold forging metal between two dies. The process is widely used in the manufacturing of bolts, screws, and other threaded components. The blank diameter used in thread rolling plays a critical role in determining the quality and accuracy of the thread.

The blank diameter refers to the diameter of the raw material before the thread is formed. In thread rolling, the blank diameter must be carefully selected to ensure that the final thread meets the required specifications.

Pitch Diameter and Minor Diameter
Before understanding the selection of the blank diameter, it is essential to understand two critical terms associated with threads - pitch diameter and minor diameter.

Pitch diameter is the theoretical diameter of the thread, which is determined by the distance between the crests of two adjacent threads. It is the most critical dimension of the thread and is used to determine the thread's tolerance and fit.

Minor diameter, on the other hand, is the smallest diameter of the thread, which is measured at the bottom of the groove. It is essential to ensure that the minor diameter is not too small, as it can lead to thread failure due to fatigue or stress concentration.

Selection of Blank Diameter
Now that we understand the importance of pitch diameter and minor diameter let's discuss the selection of the blank diameter.

The blank diameter used in thread rolling is typically equal to the pitch diameter of the thread. This is because thread rolling displaces the material, causing it to flow and fill the dies' cavities. As a result, the material's diameter increases, and the final thread's pitch diameter matches the blank diameter.

It is crucial to note that the blank diameter must be carefully selected to ensure that the final thread meets the required specifications. If the blank diameter is too small, the thread's minor diameter may be too small, leading to thread failure. On the other hand, if the blank diameter is too large, the material may not flow correctly, leading to poor thread quality.

Conclusion
In summary, the blank diameter used in thread rolling is typically equal to the pitch diameter of the thread. This ensures that the final thread's pitch diameter matches the required specifications. However, the blank diameter must be carefully selected to ensure that the thread's minor diameter is not too small, leading to thread failure, or too large, leading to poor thread quality.