How to Drill Out a Broken Bolt (Step-by-Step Guide)

<h1>How to Drill Out a Broken Bolt (Step-by-Step Guide)</h1>

<p>When a bolt snaps off flush — or below the surface — drilling it out is often the only way forward without destroying the part. Done right, you can extract a broken bolt and save the original threads. Done wrong, you drill off-center and turn a simple repair into a major one. This guide shows the correct tools, technique, and order of operations to drill out a broken bolt safely.</p>

<h2>Before You Drill: Try the Easy Fixes First</h2>

<p>Drilling is a last resort. If any of the broken bolt still sticks out, try these first:</p>

<ul>

<li>Soak the threads in penetrating oil for 15–30 minutes (longer for rust).</li>

<li>Grip the stub with locking pliers and back it out gently.</li>

<li>If the head sheared but the shank protrudes, the released tension often lets it spin out by hand.</li>

</ul>

<p>If the bolt is flush or recessed, move on to drilling.</p>

<h2>Tools You'll Need</h2>

<ul>

<li>Center punch and hammer</li>

<li>Variable-speed drill</li>

<li>Left-hand drill bits (these alone often remove the bolt)</li>

<li>Screw extractor set (easy-out)</li>

<li>Penetrating oil</li>

<li>Cutting fluid</li>

<li>Safety glasses</li>

</ul>

<div class="my-6"><img src="https://images.unsplash.com/photo-1518709414768-a88981a4515d?w=1000&q=80&auto=format&fit=crop" alt="Drilling into metal in a workshop" loading="lazy" decoding="async" class="w-full rounded-xl shadow-lg" /><span class="block text-sm text-muted-foreground mt-2 text-center italic">Drilling into metal in a workshop.</span></div>

<h2>Step-by-Step: Drilling Out a Broken Bolt</h2>

<h3>Step 1: Grind or File the Surface Flat</h3>

<p>If the break is uneven, file or grind the top of the bolt flat. A flat surface keeps your drill bit from wandering off-center — the single most important factor in a clean extraction.</p>

<h3>Step 2: Center Punch the Exact Middle</h3>

<p>Mark the dead center of the bolt with a center punch. This divot guides the drill bit and stops it from skating. ⚠️ <strong>An off-center hole will damage the surrounding threads — take your time here.</strong></p>

<h3>Step 3: Drill a Pilot Hole with a Left-Hand Bit</h3>

<p>Start with a small left-hand drill bit running the drill in reverse. Apply steady pressure and cutting fluid. Frequently, the heat and counter-clockwise bite of the left-hand bit grab the bolt and spin it right out — no extractor needed.</p>

<h3>Step 4: Enlarge the Hole (If Needed)</h3>

<p>If the bolt doesn't back out, step up through progressively larger bits until the hole is sized for your extractor. Stay centered and stop well before the bit reaches the bolt's thread diameter so you don't cut the part's threads.</p>

<h3>Step 5: Use a Screw Extractor</h3>

<p>Tap the extractor into the pilot hole. Turn it counter-clockwise with a tap handle or wrench. As it bites deeper, it should thread the broken bolt out. Go slow and steady — extractors are hardened and brittle, and a snapped extractor inside the hole is much harder to remove than the bolt was.</p>

<h2>Drill Bit Size Guide</h2>

<p>Match your pilot bit and extractor to the broken bolt's size:</p>

| Bolt Size | Pilot Drill Bit | Extractor Size |

| --- | --- | --- |

| 1/4 in / M6 | 1/8 in | #1 |

| 5/16 in / M8 | 5/32 in | #2 |

| 3/8 in / M10 | 3/16 in | #3 |

| 1/2 in / M12 | 1/4 in | #4 |

<h2>If the Bolt Is Seized or Rusted</h2>

<p>For corroded bolts, heat helps break the rust bond. Apply a propane torch to the surrounding metal (not the bolt) for a few seconds, let it cool slightly, then reapply penetrating oil — the thermal cycling draws oil into the threads. Repeat before drilling.</p>

<h2>Common Mistakes to Avoid</h2>

<ul>

<li><strong>Drilling off-center:</strong> ruins the host threads — punch carefully.</li>

<li><strong>Skipping cutting fluid:</strong> overheats and dulls bits, and work-hardens the bolt.</li>

<li><strong>Forcing the extractor:</strong> a snapped extractor is hardened steel and nearly impossible to drill.</li>

<li><strong>Drilling too large:</strong> cutting into the part's threads turns a bolt extraction into a thread repair.</li>

</ul>

<h2>When Threads Are Damaged</h2>

<p>If the threads tear out during extraction, don't panic — you can restore them with a thread insert. See our guide to <a href="/blog/common-fastener-problems-solutions">common fastener problems and how to fix them</a> for installing inserts and chasing damaged threads.</p>

<div class="bg-primary/5 border border-primary/20 rounded-xl p-5 my-6"><span class="block font-semibold text-gray-900 mb-1">Not sure what fastener you're dealing with?</span><span class="block mb-3">Identify the broken bolt first so you can size your drill bit, extractor, and replacement correctly. Snap a photo and our <a href="https://www.whatsizebolt.com/ai-bolt-identifier/"><strong>AI Bolt Identifier</strong></a> will identify the size, thread, and type in seconds.</span><span class="block"><a href="https://www.whatsizebolt.com/ai-bolt-identifier/"><strong>Identify your bolt with AI →</strong></a></span></div>

<h2>Frequently Asked Questions</h2>

<h3>Can you drill out a bolt without an extractor?</h3>

<p>Often, yes. A left-hand drill bit run in reverse frequently grabs the bolt and backs it out on its own, which is why pros reach for them first.</p>

<h3>What size drill bit for a broken bolt?</h3>

<p>Start small — roughly half the bolt's diameter — and step up only as needed. See the size chart above for common bolt sizes.</p>

<h3>Why does my drill bit keep slipping off the bolt?</h3>

<p>The surface isn't flat or the center punch mark is too shallow. File the top flat and make a deeper punch divot before drilling.</p>

<p>Need to identify the bolt before you start? Use our <a href="/blog/how-to-measure-bolt-size-a-complete-guide-for-mechanics-and-diyers">bolt measurement guide</a> to size the replacement.</p>