Screw Thread Kits and Inserts: Left Hand
Left hand screw threads inserts are used to produce new threads or can be used to repair threaded holes which have been damaged or stripped or crossthreaded and refurnish them to their original thread size.
The left hand insert, which is larger in diameter than the tapped hole is compressed during installation then allowed go spring back, permanently anchoring the insert in the tapped hole.
Because of the larger diameter, the insert has a greater contact area and is normally stronger than the original threads