The flank angle refers to the angle measured between the two flanks of a thread profile—that is, between the lateral surfaces that transmit forces between the screw and the nut when they are in engagement. It plays a key role in determining how much friction is generated in the thread and how efficiently rotational motion is converted into linear motion.
Typical values depending on the type of thread
- Metric ISO thread (tapered thread, DIN 13): 60°
- Trapezoidal thread (Tr, DIN 103): 30°
- Saw thread (S, DIN 513): asymmetrical, approx. 3° lead angle / 30° back angle
- Round thread (DIN 405): 30°
- Whitworth thread: 55°
Significance for Function
A small flank angle reduces friction between the thread flanks, thereby increasing efficiency. Such profiles are suitable for motion threads that need to be adjusted frequently and with as little effort as possible. A large flank angle, on the other hand, increases friction and thus self-locking, which prevents unintentional loosening in fastening threads.
Practical Applications of Trapezoidal Threads
For trapezoidal lead screws in accordance with DIN 103, the standardized flank angle of 30° ensures a balanced ratio of load-carrying capacity, wear resistance, and efficiency. It thus directly affects the achievable self-locking capability and the required drive torque, making it a key design parameter when selecting the appropriate thread profile. In ball screws, a comparable parameter is referred to as the contact angle, since in this case balls—rather than thread flanks—transmit the forces.