What type of thread is primarily used for bolts, nuts, and set screws?

The type of thread primarily used for bolts, nuts, and set screws is the ISO thread, also known as the metric thread. ISO threads provide a standardized system for sizes and pitches, which is essential for ensuring compatibility between fasteners, such as bolts and nuts. This standardization allows for easier manufacturing and assembly in engineering applications.

ISO threads have a symmetrical profile that contributes to effective load distribution and strength in fastening applications. They are characterized by a 60-degree thread angle and are commonly found in a variety of engineering and construction contexts, making them suitable for general-purpose use.

In contrast, the other types of threads mentioned have specific applications that make them less suitable for general fastening purposes. Acme threads are primarily used for linear movement applications, such as lead screws, due to their trapezoidal shape which provides greater surface contact and strength, while square threads are used for similar reasons. Buttress threads are designed for high axial loads in one direction, typically used in clamping devices or applications that require strength in one load direction, but they lack versatility compared to ISO threads.