How to Loosen a Stuck or Rusted Bolt: 7 Steps in Order, From Grip to Heat (and the Right Tool for Each)

November 3, 2026

Quick answer: work up from gentle to forceful, and stop before you round the head

Grip it properly first: a 6-point socket or box-end wrench, not an open-end wrench or a worn 12-point socket. 6-point tools bear on the flats of the hex, so they are less likely to round it off (MISUMI USA).
If it is rusted: soak it with a penetrating oil made for rust and give it time to work before you pull hard.
If it needs more force: a longer breaker bar, not a pipe slipped over a ratchet. Doubling the handle length doubles the torque for the same pull.
If steady force does nothing: add shock. A hand impact driver struck with a hammer, or an impact wrench with impact-rated sockets only.
If it was assembled with red threadlocker: it needs local heat above 250 °C (about 480 °F) before it will turn (Henkel/LOCTITE).
If the head is already rounded: switch to an extractor made for that head, or cut it off.

A bolt usually sticks for one of three reasons: rust or corrosion in the threads, overtightening, or a thread-locking compound. Fastenal lists moisture, corrosion, overtightening and long periods without movement as the usual causes. The fix depends on which one you are fighting, and the order matters: every failed attempt with the wrong tool makes the next one harder, because the head starts to round.

This guide puts the methods in order and names the type of tool each step needs. We run a tool shop, so where a step needs a tool we stock, we link it. Where it needs something we do not sell (penetrating oil, a torch, an impact wrench, a nut splitter), we say so and describe what to look for from any brand. Sources are listed at the end.

Which step to start with

What you see	Start with	Tool type	In our store?
Bolt turns a little with a normal wrench, then stops	Step 1: correct grip	6-point socket or box-end wrench	Yes, sockets
Visible rust around the head or nut	Step 2: penetrating oil	Rust penetrant (any brand)	No
Clean bolt, just very tight	Step 3: leverage	Breaker bar	Yes, breaker bars
Steady force does nothing	Step 4: shock	Hand impact driver, or impact wrench with impact sockets	Hand impact drivers and impact sockets; impact wrenches no
Blue or red residue on the threads	Step 5: heat	Torch or heat source	No
Hex socket (Allen) head rounded out	Step 6: extractor	Hex socket extractor bit	Yes, Neji-Mogura
Outside hex rounded, or nothing works	Step 7: last resort	Bolt extractor socket, nut splitter, cut-off tool	No

Before you start: make sure you are turning it the loosening way. Most bolts loosen counter-clockwise, but some fasteners use left-hand threads, so check the service manual if a bolt on a machine or vehicle refuses to move. Wear eye protection, and if the bolt is on anything electrical, isolate the power first.

ENGINEER DBZ-20 Screwzaurus Mole 4-Piece Set

Step 1: get a grip that will not round the head

A 6-point socket matches the six sides of a hex head and grips the flats rather than the corners, which spreads the torque and reduces slipping and rounding. MISUMI USA recommends 6-point sockets for heavy-duty work and stuck fasteners, and 12-point sockets for tight spaces where you need a shorter swing. An open-end wrench touches only two flats, so it is more likely to slip on a tight bolt than a 6-point socket or box-end wrench.

The socket must also fit snugly: use the exact size (metric or inch) of the head, push the socket fully onto the head, and keep the handle square to the bolt so the socket does not tilt off.

If you need a set, the Ko-ken 3286Z is a 3/8" drive set with 14 six-point sockets from 7 to 22 mm, and it already includes a 250 mm breaker bar (3768Z-250). For other drive sizes and inch sets, see Best Socket Set by Job.

Ko-ken 3286Z 6-point socket set with breaker bar — A full set of 6-point sockets with its own 250 mm breaker bar: the Ko-ken 3286Z.

Step 2: penetrating oil, and patience

For rusted threads, a penetrating oil made for corrosion is the usual first chemical step. WD-40 says to spray its Specialist Fast Release Penetrant under the bolt head and around the nut, then tap the bolt lightly so it works into the threads. Other widely sold penetrants include PB B'laster, Liquid Wrench and Kroil. We do not sell penetrating oils, and we have not tested one against another, so we do not rank them.

What matters more than the brand is time. Apply it, give it time to soak into the threads, then try again, and repeat for heavy rust. Pulling hard on a bolt the oil has not reached yet only increases the risk of rounding or snapping it.

Step 3: more leverage, the right way

Torque is force multiplied by the length of the lever. So the simplest way to get more torque without pulling harder is a longer handle. That is what a breaker bar is: a solid bar with a pivoting drive head and no ratchet mechanism inside to break.

Do not slip a pipe over a ratchet. A pipe extension (a "cheater bar") multiplies the load on the tool as well as on the bolt. Even sources that accept a cheater on a breaker bar draw the line at a ratchet, because the ratchet mechanism is far more likely to break (Wikipedia, citing workshop practice). Engineering guidance also warns that torque far beyond a tool's design capacity can bend the handle or shatter the socket. Use a longer breaker bar instead, and keep a torque wrench out of this job altogether: it is a measuring tool, not a breaker bar.

How much difference does length make?

The table shows the torque you get from the same 100 N pull (about 22 lbf) at the end of each bar. Calculation: torque (N·m) = 100 N × overall length (m). Your hand sits a little inside the end, so real figures are slightly lower; the point is the comparison.

Breaker bar	Drive	Overall length	Torque from a 100 N pull	Weight	Origin
Ko-ken 4768N-300	1/2"	300 mm	30 N·m (22 ft·lb)	600 g	Japan
Ko-ken 4768Z-430 Z-EAL	1/2"	430 mm	43 N·m (32 ft·lb)	720 g	Japan
Ko-ken 4768N-450	1/2"	450 mm	45 N·m (33 ft·lb)	784 g	Japan
Ko-ken 4768N-600	1/2"	600 mm	60 N·m (44 ft·lb)	1,100 g	Japan
KTC BS4-780	1/2"	785.8 mm	79 N·m (58 ft·lb)	1,500 g	Japan

Lengths, weights and country of origin are from our product pages (TRUSCO data); the Ko-ken 4768N lengths match Ko-ken's US distributor, Freer Tool. The 600 mm bar gives twice the torque of the 300 mm bar for the same effort. A 380 mm version, the 4768N-380, sits between them.

Ko-ken 4768N-600 600 mm breaker bar — Left: Ko-ken 4768N-600 (600 mm, 60 N·m from a 100 N pull). Right: KTC BS4-780 (785.8 mm, 79 N·m).

KTC BS4-780 785.8 mm breaker bar — Left: Ko-ken 4768N-600 (600 mm, 60 N·m from a 100 N pull). Right: KTC BS4-780 (785.8 mm, 79 N·m).

Which length? Longer is not always better: it needs room to swing, and it can deliver enough torque to snap a small bolt. So choose the longest bar that has room to swing where the bolt is, and match the drive size to the fastener: a 3/8" bar like the one in the 3286Z set for smaller bolts, a 1/2" bar for larger ones. Any well-made 1/2" breaker bar from any brand does the same job; drive size and length matter more than the name on it.

Technique: set the socket fully on the head, position yourself so you pull rather than push where you can, and pull smoothly. If it does not move with steady force, stop and go to Step 4 rather than adding more force, which risks snapping the bolt.

Step 4: add shock instead of more force

A sharp blow can break a rust bond that steady force will not. There are two ways to deliver it.

A hand impact driver (no power needed)

A hand impact driver turns a hammer blow into a short burst of turning force. Ko-ken's US distributor describes the Ko-ken Attack Driver as converting hammering strength into torque by an instant shock to its head, and says it works with bits or sockets for screws or bolts. The Ko-ken 4112G takes 1/2" drive sockets (163 mm, chrome molybdenum steel, 810 g on our product page); the 3112G is the 3/8" version. Set it to the loosening direction, hold it firmly on the socket, and strike the back squarely with a hammer.

Ko-ken 4112G Attack Driver 1/2 inch — Hammer-driven impact drivers: Ko-ken 4112G (1/2") and 3112G (3/8"). No battery, no air line.

Ko-ken 3112G Attack Driver 3/8 inch — Hammer-driven impact drivers: Ko-ken 4112G (1/2") and 3112G (3/8"). No battery, no air line.

For stuck screws rather than bolts, see Best Manual Impact Driver for Stuck Screws, which compares 17 models.

An impact wrench (power tool)

A cordless or air impact wrench hammers continuously and is the usual shop answer for large rusted fasteners. We do not sell impact wrenches. If you use one, use impact sockets only: Snap-on warns that chrome hand sockets must never be used on impact tools, and suppliers explain that impact sockets are made from tougher chrome molybdenum steel, while standard chrome vanadium hand sockets can crack or shatter under impact. We stock impact sockets from Ko-ken and KTC; see also Best Impact Socket Set by Job.

KTC BP8-21P impact socket — An impact socket (KTC BP8-21P, 1" drive).

Step 5: heat, especially for threadlocker

Heat expands the metal around the bolt and can break a rust bond. It is also the method Henkel, which makes LOCTITE, recommends for red (high-strength) threadlocker: apply localized heat above 250 °C (about 480 °F; its English guide lists 550 °F) and unthread the bolt while it is hot. Henkel warns that without heat some bolts in tapped holes risk breaking, and adds that even aggressive solvents cannot weaken a cured red threadlocker.

We do not sell torches. Keep any flame away from fuel and brake lines, rubber, plastics and anything flammable, and let parts cool before handling.

Step 6: the head is rounded out (hex socket bolts)

When a hex key spins inside a hex socket (Allen) bolt, the socket has rounded into a circle and a normal key will not grip again. The Japanese maker ENGINEER makes the Neji-Mogura ("screw mole") bit for this. The ENGINEER DBZ-20 Neji-Mogura set has four bits for hex sockets of 2, 2.5–3, 4 and 5 mm across flats; ENGINEER says they remove damaged hex socket screws without hammering and can be used in a power driver. Single bits are also available, such as the DBZ-425 for a 2.5 mm hex.

ENGINEER DBZ-20 Neji-Mogura bits — ENGINEER Neji-Mogura bits bite into a rounded hex socket so you can turn the bolt out.

Before using any extractor on a seized bolt, go back through Steps 2, 4 and 5. An extractor that has to fight rust as well as a damaged head is far more likely to slip or break. For cross-head and slotted screws, see How to Remove a Stripped Screw.

Step 7: last resort, when the outside hex is rounded

If the outside of a hex head or nut has rounded, the usual tools are bolt extractor sockets (reverse-spiral sockets that bite into the rounded head, sold by several brands such as IRWIN) or, for a nut, a nut splitter that cracks the nut so it can be removed. We do not stock either. Fastenal notes that when time is short, cutting the bolt off and replacing it may be the quickest fix, and that drilling it out and re-tapping the hole is a reliable fallback.

How to stop it happening next time

Tighten to the specified torque with a torque wrench rather than by feel; overtightening is one of the causes Fastenal lists. See How to Use a Torque Wrench.
Use the threadlocker strength the manual specifies; red is a high-strength product that LOCTITE treats as permanent unless heated.
Keep 6-point sockets for anything that is tight, rusted or high-torque.

Ko-ken 4768N-450 1/2 inch drive breaker bar

All-round breaker barKo-ken 4768N-450

1/2" drive, 450 mm, chrome molybdenum steel, made in Japan.

View 4768N-450

KTC BS4-780 extra-long 1/2 inch drive breaker bar

Maximum leverageKTC BS4-780

1/2" drive, 785.8 mm overall, about 2.6× the torque of a 300 mm bar for the same pull.

View BS4-780

Ko-ken 4112G Attack Driver hand impact driver 1/2 inch drive

Shock without powerKo-ken 4112G Attack Driver

Hand impact driver for 1/2" sockets or bits, 163 mm, made in Japan.

View 4112G

Ko-ken 3286Z Z-EAL 3/8 inch drive 6-point socket set

6-point socketsKo-ken 3286Z Z-EAL set

14 six-point sockets 7–22 mm with a 250 mm breaker bar, made in Japan.

View 3286Z

ENGINEER DBZ-20 Neji-Mogura hex bolt extractor bit set

Rounded hex socketsENGINEER DBZ-20 Neji-Mogura

Four bits for rounded hex sockets of 2 to 5 mm, made in Japan.

View DBZ-20

FAQ

Can I put a pipe over my ratchet for more leverage?

The usual workshop advice is no: use a breaker bar. A ratchet's internal mechanism is the weak point, and even sources that tolerate a pipe on a breaker bar advise against it on a ratchet (Wikipedia). A longer breaker bar gives the same extra torque without the risk.

Should I use a 6-point or 12-point socket on a rusted bolt?

Mechanics debate this. For a rusted or very tight bolt, though, the common advice is still to reach for a 6-point socket first, and MISUMI USA recommends 6-point sockets for stuck fasteners. Keep 12-point sockets for 12-point heads and tight spaces.

Does WD-40 loosen a rusted bolt?

WD-40 sells a dedicated product for this, WD-40 Specialist Fast Release Penetrant, and says to spray it under the bolt head and around the nut, then tap the bolt lightly so it works into the threads. Whatever penetrant you use, give it time and repeat if needed.

How hot does a bolt need to be to release red Loctite?

Henkel says to apply localized heat above 250 °C (about 480 °F; its English guide lists 550 °F) and unthread the bolt while it is hot.

Can I use regular sockets on an impact wrench?

No. Snap-on warns that chrome hand sockets must not be used on impact tools; use impact sockets, which are made from tougher steel for repeated blows.