Types of Threaded Fasteners

Threaded connections are widely used, detachable fastening methods valued for their simple structure, reliability, and ease of assembly and disassembly. Traditional inspection methods-such as using thread gauges for contact measurement or universal tool microscopes for manual measurement-are labor-intensive, inefficient, and prone to human error.

Threads can be classified by the shape of their profile into triangular, rectangular, trapezoidal, and buttress threads. They are also categorized by the direction of the helix: right-hand threads (where the helix rises to the right when the thread is held upright) and left-hand threads (where it rises to the left). Right-hand threads are standard in mechanical manufacturing, while left-hand threads are used only when specific requirements dictate. Additionally, threads are classified by the number of helix starts into single-start threads and multi-start threads (with equally spaced starts). For ease of manufacturing, threads typically do not exceed four starts.