Buttress threads are commonly used in which type of application?

Buttress threads are designed specifically to handle axial loads in one direction, making them ideal for applications where force is predominantly applied along the axis of the screw. This characteristic is particularly beneficial in machinery lead screws, where the primary function is to provide precise linear motion and support heavy loads without the risk of stripping or deformation.

The design of buttress threads incorporates a steep incline on one side and a shallow incline on the opposite side, creating a strong, stable engagement ideal for applications in machinery lead screws. This design allows them to effectively transmit force during operation, especially in machinery settings where high torque and significant loads are common.

The other options illustrate applications where different thread types are more suitable. For instance, lead screws in lathes typically utilize acme threads for better engagement in both directions, while screw jacks may use trapezoidal threads for efficiency in lifting. Metric threads used in bolts are generally standardized and optimized for fastening rather than for delivering load support in a unidirectional manner. Thus, the unique properties of buttress threads make them the most appropriate choice in machinery lead screw applications.