Glossary

Cross threading is a fastening defect that occurs when the male and female threads of a fastener (such as a bolt and nut, or a screw and tapped hole) do not align properly during installation. Instead of the threads engaging smoothly, the fastener is driven in at an angle, forcing the threads to cut across each other. This damages the thread profiles and creates a misaligned, unstable joint.

When cross threading happens, the fastener may feel tight prematurely, even though it hasn’t been seated correctly. This false sense of tightness is dangerous because the joint may not have sufficient clamping force and can fail under load. Additionally, cross threading often causes permanent damage to both the fastener and the mating component, especially if they are made of softer materials like aluminum or plastic.

Cross threading is common when bolts or screws are started with too much force or at the wrong angle, or when power tools are used carelessly without first aligning the threads by hand. To prevent it, fasteners are typically started by hand until several threads are engaged smoothly before applying torque with a wrench, screwdriver, or power driver. Using lubricants, proper alignment, and thread guides can also reduce the risk.

Because cross threading compromises both the strength and integrity of the joint, damaged parts usually need to be repaired (e.g., with a thread chaser, tap and die, or helicoil insert) or replaced entirely.