How to Unscrew a Stripped Bolt: Step-by-Step Guide

A stripped bolt head turns a 10 minute repair into an afternoon-long battle, but with the right sequence of techniques you can almost always back it out without resorting to a grinder. The trick to how to unscrew a stripped bolt is starting with the least destructive method and escalating only when the previous step fails. This guide walks through seven approaches in the exact order a working mechanic uses them, with the tools, costs, and trade-offs for each one.

Step 1: Diagnose How Bad It Is

Look at the bolt head with a flashlight. If the corners on a hex head are merely rounded but the flats still have shape, you can probably catch it with a smaller socket or vise grips. If the head is fully circular, you need an extractor. If the head is sheared off entirely, jump to the cobalt drill bit section near the end. Spending 30 seconds on diagnosis saves an hour of guessing.

Hit the bolt with a wire brush to clear rust and grease so you can see the metal clearly. A rusted-but-intact head responds to penetrant. A truly rounded head needs mechanical bite.

Step 2: Soak With Penetrating Oil

Penetrating oil reduces the torque required to break a bolt loose by 30 to 60 percent. The best products in independent testing are Kroil Original, PB B’laster, and Aero Kroil. Liquid Wrench and WD-40 Specialist Rust Release work in a pinch but soak slower.

Spray the bolt and the threads underneath, then walk away for 20 minutes. For badly seized bolts, soak overnight and reapply every six hours. Tap the bolt head gently with a hammer between soaks to send vibration down the threads and pull oil deeper.

Step 3: Try a Rubber Band or Steel Wool

For a lightly stripped Phillips or hex socket, press a wide rubber band — a thick #84 office band or a square cut from a bike inner tube — over the head before inserting the driver. The rubber fills the gap and gives the bit something to bite. Steel wool works the same way for hex sockets, packed into the recess and then the Allen key driven in firmly.

Press straight down with your full body weight while turning slowly. Most lightly stripped fasteners pop loose this way without a single specialty tool.

Step 4: Step Down a Socket Size

If the bolt head is rounded but still 3D, grab a 6-point socket one size smaller than the original and hammer it onto the head. A 14mm 6-point on a stripped 15mm head, or a 9/16 on a stripped 5/8, will bite the corners that remain. Use a deadblow or rubber mallet to seat the socket, then turn with a 1/2 inch breaker bar for maximum leverage.

Always reach for 6-point sockets here. 12-point geometry rounds the corners further instead of biting them.

Step 5: Bolt Extractor Sockets

Irwin Bolt-Grip Hanson 11119 5-piece set, around $30, or the Gearwrench 84784 set, around $55, replace your sockets for the stripped fastener only. The internal spiral teeth bite harder as you turn counterclockwise. These work on bolts down to about 70 percent of original head diameter.

Drive the extractor on with a hammer, attach a ratchet or breaker bar, and turn slowly with steady pressure. Hammering during the turn shocks the threads loose. Expect to ruin the extractor on the bolt — they are sacrificial tools, not lifetime sockets.

Step 6: Vise Grips and Pipe Wrench

For exposed bolts where you can grip the sides of the head, locking pliers solve the problem fast. Irwin 10WR Curved Jaw 10-inch vise grips, around $24, clamp onto a rounded head with adjustable bite pressure. Set the rear screw tight, clamp the jaws, then turn the entire tool counterclockwise.

A 14-inch pipe wrench gives even more leverage if the bolt protrudes far enough from the surface. Pipe wrench teeth dig harder the more torque you apply, which is exactly what a frozen bolt needs.

Step 7: Heat and Wax

For bolts threaded into cast iron, aluminum, or steel that has rusted into place, heat changes everything. Apply MAP gas or a propane torch to the surrounding material for 30 to 60 seconds. As the metal expands, touch a paraffin candle or beeswax stick to the threads at the joint. Capillary action pulls melted wax down the threads, lubricating them as they cool.

Be careful around fuel lines, gaskets, and painted surfaces. A heat shield made from a sheet of aluminum flashing protects nearby parts. Never use this method on a bolt holding plastic or polymer assemblies.

Step 8: Drill and Use a Spiral Extractor

When the head is sheared or fully cammed out, drill straight down the center of the bolt with a cobalt 1/8 inch bit, then step up to 3/16 and 1/4. Insert a spiral bolt extractor like the Irwin Hanson 53227 or a Snap-on EXLS5 into the pilot hole, tap it in with a hammer, and turn counterclockwise with a tap handle.

Keep the drill bit perpendicular. A crooked pilot hole makes extraction nearly impossible. Use cutting oil to extend bit life and slow the RPM to about 400 to avoid burning the bit tip.

Last Resort: Drill It Out Entirely

If extractors fail, drill the bolt out completely using progressively larger bits until you reach the minor thread diameter, then chase the threads with the appropriate tap. For a 1/4-20 bolt, drill to 13/64 and run a 1/4-20 tap. For metric M8, drill to 6.8mm and use an M8x1.25 tap.

This destroys the bolt and risks the female threads, but on a properly aligned pilot hole the original tapped hole survives 80 percent of the time. Plan on having Heli-Coil thread inserts on hand in case the female threads damage during cleanup.

Prevention for Next Time

Apply anti-seize compound, Loctite 567 or Permatex 80078, to threads on any bolt that may need to come back out. Use 6-point sockets exclusively. Buy quality fasteners — Grade 8 USA-made bolts strip far less than imported Grade 5. Knowing how to unscrew a stripped bolt is useful, but never needing to use that knowledge is even better.