threadstripping

Threadstripping is a failure mode in threaded fastener assemblies where the engagement between male and female threads is damaged or worn to the point that it can no longer carry load. This results in a significant loss of clamping force and may allow a fastener to loosen or withdraw under service stresses. Threadstripping can occur with external threads (bolts, screws) or internal threads (nut, tapped hole) and is often more about the thread profile being compromised than the nut or bolt breaking.

Common causes include overtightening beyond the material’s shear strength, cross-threading during installation, prolonged vibration, corrosion, wear from repeated assembly and disassembly, and using an incompatible thread size or pitch. Inadequate lubrication can either increase friction and peak torque or, if misapplied, promote movement that damages threads. Poor preparation of mating surfaces, damaged hole walls, or remnants of debris can also initiate stripping.

Detection symptoms are reduced torque resistance, the fastener spinning without drawing in, visible flattening or galling of threads, and persistent loosening after tightening to specification. Prevention focuses on proper torque specifications, appropriate lubrication, using correct thread class and engagement length, and avoiding reuse of damaged components. For damaged threads, repairs include chasing or cleaning threads, re-tapping to a larger size, or installing thread inserts (such as helicoils or Keenserts) to restore engagement. In critical applications, thread repairs follow industry standards and may require part replacement rather than reuse.