How to Break a U Lock

Co-authored by wikiHow Staff

Last Updated: July 23, 2022

Even though U-locks are designed to be unbreakable, there are several ways to get one open if you've lost your key. This is good news if your lock is attached to your bike or another possession that you need unlocked. The easiest way to break a U-lock is by using simple ballpoint pen to jimmy the lock. There are other ways that you can unlock the U-lock that require the use of force, and will actually break the structure of the lock and make it henceforth unusable. For this reason, it's always best to try to jimmy the lock before actually breaking the U-lock.

Method 1

Method 1 of 3:

Opening a U-lock With a Ballpoint Pen

1
Find a basic ballpoint pen. A basic ballpoint pen is the best tool for opening a locked U-lock. Find a standard “stick” pen, usually the cheapest types of pens that have the ballpoint on one end, a small cap to cover the other end of the pen, and a separate cover that you put on the pen when not using it.^{[1]
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- Make sure to use a cheap pen, as opposed to a more fancy kind. You need to find a pen that has an end cap that pops off, rather than one that screws off or can't be easily removed.
2
Remove the cap from the end of the pen. Use your fingernails to pry off the small cap on the end of the pen. Removing the cap will leave you with an open tube that is roughly the same diameter as a standard U-lock key.^{[2]
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3
Insert the tube of the pen into the U-lock keyhole. After you remove the cap, insert the end of the pen with the open tube into the keyhole of your U-lock. It should comfortably fit within the hole.^{[3]
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- If the tube of the pen doesn't fit inside the keyhole, it won't work to open the lock. Find a pen that fits inside keyhole after its cap has been removed.
4
Push and twist the pen inside the keyhole. Hold the U-lock with your non-dominant hand. With your dominant hand, grip the ballpoint pen and twist it inside the lock while pushing firmly.
- Use your wrist rather than your whole arm to get the energy needed to push and twist.
5
Twist until the U-lock unlocks. Keep twisting the pen, shaking the bar of the U-lock a little bit to add pressure. You may have to do this anywhere from a few seconds to a few minutes if it's your first time using this method. Twist the pen until you feel or hear the lock unlock.^{[4]
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- If you are unsure of whether the lock has opened, pull at the bar of the U-lock to check.
- If you are applying pressure, you should feel the lock open.
6
Take off the top bar of the U-lock. Pull the ballpoint pen out from the keyhole, then lift up the top bar of the lock out of the U-shaped sides. You have successfully unlocked your U-lock!^{[5]
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Method 2

Method 2 of 3:

Breaking a U-lock With a Hammer and Air Spray

1
Purchase canned air spray. U-locks are very difficult to open by hammering or using force, but they are weakened and become brittle when cooled by air spray, meaning that they can be smashed open. Buy compressed or canned air at home improvement stores or online.^{[6]
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- Canned air contains the compressed chemical difluoroethane, which will cool the lock to around -13 degrees F (-25 degrees C).
2
Position the U-lock. If your U-lock is locked but not connected to anything, breaking it will be easy. If the U-lock is locked around a bicycle or a door handle, it will a little more difficult to open, but it will still be doable.
- Position the U-lock so that the bar of the U-lock is lying flat on the ground or is against a stable surface like a door or the bar of the bike rack.
3
Spray the canned air at the keyhole of the U-lock. Hold the can of air spray about a foot away from the keyhole. Then hold down the trigger of the canned air and spray it directly at the keyhole.^{[7]
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4
Spray for about 30 seconds. Spray continuously for about 30 seconds. You will notice the bar becoming white as the chemical reacts with the surface of the U-lock and chills it.
- Be sure to aim the spray radius at the keyhole, where you will focusing your hammering.
5
Begin hammering against the keyhole. After about 30 seconds, the bar of the U-lock will have been chilled and should be brittle enough to break. Use your non-dominant hand to hold the U-lock by its loop against the ground or the surface that you positioned it against. Pick up the hammer in your dominant hand and begin to hammer against the keyhole.^{[8]
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- Keep your fingers away from the place that you are hammering. Also try to keep the U-lock stable and in position as you hammer.
- Don't be alarmed as you see the white powder on the U-lock come off in a mist as you begin to hammer.
6
Hammer until the U-lock breaks. Keep hammering against the keyhole area of the U-lock. You may have to hammer for 30 seconds or so until a piece breaks off of the bar, after which breaking it will become much easier. Focus your hammering against the broken area of the lock. More sections will come off, until the bar breaks completely and separates from one or both sides of the U.^{[9]
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- Be patient, as it may take several minutes of hammering to break the U-lock.
- Dispose of the remains of the lock when you are finished.

Method 3

Method 3 of 3:

Cutting the Lock With an Angle Grinder

1
Take the right safety precautions. An angle grinder is a power tool that is highly effective for breaking U-locks and most other kinds of locks. It's the most powerful and quick method of slicing though U-locks, but in order to handle it responsibly you need to take a few safety precautions. You practice and feel comfortable with your angle grinder before using it on your U-lock. ^{[10]
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- Put on work gloves to protect your hands, as well as goggles to stop any flyaway material from getting in your eyes.
- Don't wear any loose clothing or jewelry when you operate the angle grinder.
- Make sure that you are using the right sized disc for the grinder and that the grinder is able to go up to maximum speeds.
- If your U-lock is locked but not attached to anything, clamp it with a vice attached to a table. If the lock is fastened around a bicycle, adjust it so that when pressure is applied to it, it doesn't move but stays in relatively the same place.
2
Turn on and angle your angle grinder. Hold your angle grinder using both hands at an angle of 15-30 degrees. Hold your angle grinder a few inches away from the U-lock and turn it on.^{[11]
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3
Cut through the U-lock with the angle grinder. Use both hands to hold the angle grinder and slowly bring the blade against one of the U-shaped sides of the U-lock. Don't be alarmed when you see sparks fly; even if they touch you they won't hurt you. Hold the blade against the side of the U-lock until it cuts through. This can take anywhere from 15 seconds to a few minutes.^{[12]
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- Be very slow and deliberate when you use the angle grinder. Don't push or exert force with the grinder. Just hold the blade against the lock and wait as it chips away.
- If exert force while you cut, you will cut through the U-lock and then push angle grinder past it to cut whatever is behind the U-lock.
4
Make another cut a few inches from the first cut. If you are trying to take the U-lock off your bike or the handle of a door, you will need to create one more cut to be able to dislodge it. Use the same method to cut the U-lock as you did for the first cut, this time cutting through an area a few inches from the first cut. Stop when you complete the cut.
5
Turn off the angle grinder and remove the U-lock. After you finish using your angle grinder, turn it off. It's important as a safety precaution to turn it off immediately after you are finished using it. After you make the second cut, a section of the U-lock should have fallen away to make a gap in the lock. Take the U-lock off, store your angle grinder, and throw away the remains of your lock!

Community Q&A

Question

What if the lock has a combination?

Community Answer

You could still use a hammer and break it or you could cut it with an angle grinder.
Question

I want to keep my U lock. Can a bump key work on a Master U lock?

R2_d2000

Top Answerer

Most likely not. Most Master U locks use disk detainer locks, which are not susceptible to bump keys and are very pick-resistant. If you still have the original packaging for the lock, then you should be able to find a card with the key code, which you can then take to a locksmith or contact Master Lock to have new keys made for your U lock. If you do not have the key code, then you will most likely have to break the lock.

Warnings

Be extremely careful and always follow safety precautions when using an angle grinder.

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Never steal another person's bike by breaking their U-lock.

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Don't use your angle grinder for the first time on you U-lock. Get familiar with it before you use it to break the lock.

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