The concept of thread starts refers to the number of distinct, continuous helical grooves that spiral around the cylindrical surface of a screw or bolt. Each start represents a separate spiral thread that advances along the length of the fastener.
In a single-start thread, there is only one continuous spiral, advancing by the thread pitch with each full turn. In multi-start threads, such as double-start or triple-start, multiple helical grooves run in parallel around the fastener. For instance, a double-start thread has two parallel spirals, and a triple-start thread has three.
The number of starts influences the thread’s lead, which is the distance the thread advances in one complete turn. In multi-start threads, the lead is a multiple of the pitch, determined by the number of starts. This configuration affects how the load is distributed across the threads and can enhance assembly speed, as multi-start threads advance more with each turn compared to single-start threads. Understanding thread starts is crucial for designing threads that meet specific performance needs and ensuring effective function in various applications.