The only thing more stressful than a rusty, seized bolt is the sickening feeling you get when you hear a pop followed by the removal of only a portion of the bolt or screw. Now what? Well, with a bit of patience and the correct tools, you can extract that ornery piece of scrap metal and roll on.
Before we discuss what to do when a bolt breaks, maybe it is best to begin with some tips on how not to break them in the first place. The first time I ever broke a bolt off, I was 16. I was so proud that I had completed my first brake pad replacement on my car. I was snugging up the calipers on the first set and, to save time, I was using Dad’s impact wrench. It doesn’t take much to imagine what occurred next.
Yup … I over-tightened the little booger and “pop” – off with its head. I remember it well; the worst part was not breaking the bolt but telling and then showing Dad what I had done. It turned into more of a job than I anticipated, but I did learn a valuable lesson. There is such a thing as too much torque.
Patience is truly a virtue when dealing with a stubborn bolt. Soaking a bolt in penetrating oil or heating the bolt with a torch can help immensely. Penetrants are like lubricants but, instead, are designed to help loosen corroded or rusty connections.
There are lots of penetrants out there, and all make big claims when it comes to getting things apart. Some are more reliable than others, but I will leave that up to you to decide which is best in your book.
Oils and lubricants can act as a penetrant in many cases, but a dedicated penetrant is formulated specifically to loosen nuts and bolts. The ingredients not only soak in like oil would, they contain chemicals to eat away at the corrosion that is causing the nut or bolt to seize in its seat.
Conversely, never try to lubricate something with a penetrant; they don’t stick around like that and you can actually achieve the opposite of long-term lubrication.
OK, prevention went out the window when the bolt snapped off. There are actually several different ways to remove broken bolts and screws. Which method you use is dependent on the location of the bolt and the tools you have on hand. The first step is to assess the situation and select the method that is easiest to implement.
If the fastener is sticking up out of the metal, your problem might be as simple as flattening a side of the bolt with a grinder, heating the metal to remove rust, attaching a pair of locking pliers to the bolt and turning the little rascal out.
Of course, pretreating the fastener with a penetrating lubricant is helpful, but again – be advised that the effects are not instantaneous. It may take several hours for the oil to soak in far enough to be effective. Most times, I am not lucky enough to have a portion big enough to grip on the broken bolt, so stage two must commence.
The preparation of the visible surface of the broken fastener is our next challenge. If possible, try to polish the top of the bolt with a grinder to give you a smooth, straight surface on which to work. Regardless of whether you reach the bolt face with a grinder, the next step is to use a center punch to make a divot or depression in the center of the bolt so your drill bit will not “walk” as you drill into the bolt.
One thing you might consider is a “left-handed” drill bit set. These bits are just like traditional bits – except they are cut backward. Select a bit, left-handed or not, smaller than the diameter of the bolt but big enough so as to not break in the bolt itself, and we begin. Again, if we are fortunate, the bolt may screw out before the bit passes completely through the bolt. Regardless, it is wise to run a threading tap into the hole to straighten and clean the threads of the hole.
If you don’t have left-handed drill bits, you should have an easy-out set. These are little hardened bits with twisted flutes arranged in a left-hand pattern. The top of each bit is squared to allow turning with a wrench. The bits are tapered so the several sizes in the kit will fit a large range of bolt sizes.
The procedure is to drill into the broken shaft a short way, hammer the appropriate easy-out bit into the hole until it wedges and then turn it out with an adjustable wrench. (If you have one included in a tap-and-die set, you may select a tap handle to turn the easy-out bit.)
If all these methods fail to remove the broken bolt – yes, we’ve had this happen plenty of times over the years – then the only choice is to drill it out completely, which means drilling away the mating threads where the bolt was fastened. In this case, you will have to tap new, larger threads into the hole and find a larger bolt to use in that location.
Can’t use a larger bolt because of specific fit or appearance reasons? Well, in such cases you can obtain a Helicoil kit. A Helicoil is a ready-made threaded adapter that will screw into the larger hole you tapped. The adapter has its own internal threads of the original size, so the proper fastener can be used. Helicoil kits are available wherever you find easy-out kits (good hardware stores, tool stores, online, etc.). 
Andy Overbay holds a Ph.D. in ag education and has more than 40 years of hands-on dairy and farming experience.
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Andy Overbay
- Extension Agent
- Virginia Cooperative Extension
- Email Andy Overbay
