Which type of screw thread transmits force in one direction?

• A. Square threads
• B. Buttress threads
• C. Trapezoidal threads
• D. V threads

Answer: (B)

Buttress threads are designed specifically to transmit force in one direction, making them ideal for applications where load is applied in a single direction, such as in a screw jack or during linear motion. The unique shape of the buttress thread allows it to effectively handle axial loads without significant backlash, making it efficient for applications requiring high resistance to load reversal.

In contrast, screw threads like square, trapezoidal, and V threads can transmit force in both directions or may not be as efficient in handling unidirectional loads due to their geometry and engagement. For instance, square threads offer low friction and high efficiency but are not as commonly used for unidirectional load applications as buttress threads are. Trapezoidal threads are generally used for more general-purpose applications that may require bidirectional forces, while V threads are typically not optimized for load directionality as they are used more for fastening rather than force transmission. Thus, buttress threads stand out in their ability to effectively transmit force reliably in one direction.