Transmission in one direction refers to the requirement of a thread profile that can handle a large amount of load in one direction. The type of thread that is best suited for this purpose is the Buttress thread.

What are Buttress threads?
Buttress threads are a type of thread profile that has one side with a steep incline and the other side with a gentle slope. The steep side is designed to handle the load in one direction, while the gentle slope side is used for easy insertion and removal of the threaded component.

Advantages of Buttress threads:
1. High Load Capacity: Buttress threads have a very high load capacity in one direction due to the steep incline on one side of the thread profile. This makes it ideal for transmission applications where a large amount of load is present in one direction.

2. Efficient Power Transmission: Buttress threads are very efficient in transmitting power in one direction due to their high load capacity. This makes them ideal for applications where power needs to be transmitted efficiently in one direction.

3. Reduced Friction: The gentle slope on one side of the thread profile reduces friction during insertion and removal of the threaded component. This makes it easier to install and remove the component, reducing wear and tear on the thread profile.

4. Higher Accuracy: Buttress threads have a higher accuracy than other types of threads due to their unique shape. This makes them ideal for applications where precision is required.

Conclusion:
Buttress threads are the best type of threads for transmission applications where a large amount of load is present in one direction. They have a high load capacity, efficient power transmission, reduced friction, and higher accuracy, making them ideal for precision applications.