How can we remove a broken bolt from a tapped hole?

Question

Prepp Team · Accepted Answer

Understanding Broken Bolts in Tapped Holes

When a bolt or screw breaks off inside a tapped hole, it creates a difficult situation. The remaining piece is often flush with or below the surface, making it impossible to grip with standard tools. This broken piece obstructs the hole, preventing a new fastener from being installed. Removing it without damaging the threads of the tapped hole is crucial.

Methods for Removing Broken Bolts

Several methods can be attempted to remove a broken bolt from a tapped hole. These methods vary in effectiveness and risk to the surrounding material and threads. Let's examine some common approaches and the tools used.

Using a Tap Extractor

A tap extractor (or screw extractor/bolt extractor) is a specialized tool designed specifically for removing broken threaded fasteners like bolts or screws from holes. These tools work by gripping the inside of the broken bolt and allowing torque to be applied in the reverse direction of tightening (counter-clockwise for standard right-hand threads) to unscrew the broken piece.

There are different types of extractors, but a common type for bolts uses flutes or splines that grip the internal wall of the broken bolt or requires drilling a pilot hole into the broken bolt first before inserting a spiral flute extractor. The principle is to apply outward pressure and rotational force simultaneously.

Tool Type	How it Works	Suitability for Broken Bolts
Tap Extractor / Bolt Extractor	Grips internal surface (or drilled hole) of broken bolt and rotates it counter-clockwise.	Highly suitable, designed for this purpose.
Heat Treatment	Applying heat can expand or contract metal, sometimes loosening seized parts.	Can be risky, might affect material properties or damage surrounding area/threads. Not a direct removal tool for the broken piece itself.
Pin Punching Hammer	Used to drive pins or other objects.	Not suitable for removing a broken bolt from a tapped hole; could further wedge the bolt or damage threads/hole.
Annealing	Heat treatment process to soften metal.	Softening the bolt might make drilling easier, but it doesn't directly remove the broken piece and requires further steps (like drilling and using an extractor). Annealing the tapped hole itself isn't a method for removing the bolt.

Why Other Methods Are Not Ideal

With heat treatment: While sometimes used to loosen seized fasteners, applying heat directly to a broken bolt in a tapped hole can be tricky. Overheating could damage the threads in the tapped hole or alter the material properties of the surrounding component. It's not a direct removal tool but rather a potential aid in loosening.
With a pin punching hammer: A punch is used to drive objects. Using it on a broken bolt stuck in a tapped hole will likely just drive the bolt piece deeper or at an angle, potentially damaging the threads and making removal even harder. It's not the correct tool for extraction.
By annealing the tapped drill hole: Annealing softens metal by heating it. Annealing the *tapped hole* (the part with the threads) is generally undesirable as it could weaken the threads. While annealing the *broken bolt* itself might make it easier to drill, it doesn't remove the bolt directly and requires subsequent steps like drilling and using an extractor. Annealing the hole is incorrect for removal.

Based on the function and design of the tools and methods, a tap extractor or bolt extractor is the most appropriate tool specifically designed for removing a broken bolt from a tapped hole effectively and with minimal risk of damage to the threads.

Revision Table: Broken Bolt Removal

Problem	Recommended Tool	Outcome
Broken bolt in tapped hole	Tap Extractor / Bolt Extractor	Removes broken bolt, preserves threads.

Additional Information: Using Extractors Safely

When using a tap or bolt extractor:

Always ensure the tool is properly sized for the broken bolt.
If required, drill a pilot hole carefully down the center of the broken bolt using the correct drill bit size.
Insert the extractor straight and tap it gently to seat it firmly.
Apply steady, firm, counter-clockwise pressure. Avoid sudden jerks.
Using penetrating oil can help loosen the broken bolt before attempting extraction.
If the bolt is very tight or seized, alternative methods like drilling it out completely may be necessary, often followed by thread repair using a tap or helicoil.