Knuckle thread
![Knuckle threads have very wide rounded crests and roots. These DIN knuckle threads also use a steep thread angle.](/Images/godic/202501/22/Knuckle_Thread_Form.svg0627.png")
![This leadscrew's smooth rounded knuckle thread protects the actuator's white plastic nut from wear.](/Images/godic/202501/22/Linear_actuator_leadscrew_thread0627.jpg")
Knuckle threads are an unusual highly rounded thread form. The large space between the rounded crests and roots provides space for debris to be shifted to not interfere with the thread, making this form resistant to debris and thread damage.