What device may be used to repair a bolt hole that has been stripped out and is unable to be re-tapped?

• A. Epoxy putty
• B. Dowel pin
• C. Tap
• D. Heli-coil

Answer: (D)

When threads in a bolt hole are damaged beyond saving, you need a way to restore the internal threads so a bolt can bite again. A Helicoil is a threaded insert that fills the damaged hole and provides a new, durable internal thread for the bolt. You drill to the specified size, insert the coil with its own internal threads, and remove the tang so the bolt can engage the new threads just like it did originally. This approach preserves the hole and offers a strong, reusable repair.

Epoxy putty won’t provide a reliable, load-bearing thread. A dowel pin is used for alignment or locating, not for repairing threads. A tap is used to cut threads, but if the hole can’t be re-tapped, you need the insert to rebuild the threads rather than trying to cut new ones.