How To Remove a Rusted or Cross Threaded Screw Or Bolt
More often than not a rusted bolt or screw can bring a simple home improvement project to a screeching halt. With the right knowledge, tools, and a lot of patience, you can remove a rusted or frozen bolt and continue you project with limited frustration and delay.
There are two reasons that a screw or bolt cannot be removed:
1. Rust has formed between the screw threads and the threaded part or nut.
2. The screw or bolt was cross threaded during the initial installation.
It is important to use the correct size wrench or socket on a bolt or the correct size screwdriver tip on a screw head to make removal easier and prevent damaging the bolt or screw head.
If the problem is due to rust you should first try dissolving as much of the rust as possible. There are many rust dissolving products on the market, probably the most popular being WD-40 and Liquid Wrench, but there are many more that work just as well. These products are very thin and will flow into the threads to dissolve some of the rust and also provide some lubrication. If you do not have a commercial rust removal product available you can try hydrogen peroxide, vegetable oil, or even a soda that contains citric acid.
Spray any exposed portion of the bolt, screw, or nut that you can get to. Let it sit for 5 to 10 minutes and then gently tap on the head of the bolt or screw and housing that it is threaded into. Tapping helps the rust remover get into the threads of the bolt and the assembly.
Before using any chemicals consider the chances of staining the component or the surrounding area.
Use a wrench, socket, or screwdriver to free the bolt or screw.
If it is a bolt that is stuck in position you can try hitting the head with a hammer a few times. This will cause the bolt to vibrate and may break the rust bond that is holding it in place. If you have a hammer drill or impact wrench with a socket adapter, you can place it over the head of the bolt or the nut and use that to try to loosen the rust. If it is a screw that won't move, place a proper size screwdriver in the head, making sure it is held parallel to the screw and tap the head of the screwdriver. If the bolt is very old you can potentially break off the head so use caution.
You may also want to tighten the bolt or screw slightly to break the bond between the female and male threads.
Leverage can aid in breaking the rust bond. By using a long-handled wrench or ratchet you can generate much more force to break the rust bond. Here again too much leverage may snap the head of the bolt off rather than loosening it. You can also slip a metal pipe over the end of the handle as a “cheater” to produce more leverage.
You can use a pair of vice grips to clamp onto the head of the bolt and tap the vice grips with a hammer. You can also use vice grips or pliers on a square-shaft screwdriver to gain more leverage, but remember to apply downward force as well as twisting force to ensure that the screwdriver tip remains seated in the head of the screw, otherwise you will damage the screw head.
A box end wrench or socket provides the most consistent force on a bolt head. Adjustable wrenches or pliers are not the best tools to release a frozen bolt as they tend to slip and you have to use force to keep them on the bolt head.
If the material that the screw or bolt is threaded into is metal you can try to use heat to break the rust bond. Heat will expand metal and is best used on the nut or female portion of the assembly. Heat the assembly with a propane torch and use a hammer to hit the head of the bolt or screw a couple of times and then attempt the removal. Use a screwdriver or wrench to try to free it after heating. Wear gloves and goggles when using heat.
If you cannot heat the component the bolt or screw is in, heat the bolt or screw instead. Expanding the metal of the bolt will also help free it from the rust bond. Use caution if you have already tried chemicals or oils as they may be flammable. Take the assembly outside in a well ventilated area away from any other combustible materials.
The use of bolt or screw extractors may release the rust bond, but should only be used as a last resort. Bolt and screw extractors are designed to be used when a bolt or screw head are damaged to the point where a wrench, socket or screwdriver bit will no longer fit or seat themselves properly. They are typically used when the head of a bolt or screw has broken off.
To use a screw or bolt extractor you will need a matching drill bit for the extractor. It is a fraction of an inch smaller than the diameter of the screw as to not damage the female threads. Many bolts are made of hardened steel so you should use a quality drill bit and proceed slowly and wear goggles. It may be necessary to use a grinder to cut off the head of the bolt or screw and make the shank flat to ease drilling.
Many of the screw and bolt extractor kits come with drill bits to suit the extractor sizes.
Most screw and bolt extractors have a square end and are designed to be used with tap wrench. The end of the extractor will fit a square socket or standard box wrench, but using a tap wrench will help keep the extractor straight as it enters the hole in the screw or bolt. A tap wrench will also be needed if you have to repair any damaged threads or re-tap the hole.
Extractors can be spiral or straight fluted. Spiral extractors are left-hand threads and will dig deeper into the drilled hole as they are turned counter-clockwise and will release standard right-hand threaded bolts and screws. Only straight fluted extractors should be used with left-hand threaded screws or bolts.
After drilling out the center of the bolt, insert the extractor. Gently tap it into place and while applying downward pressure, turn the extractor counter-clockwise. You may also want to add some lubricant to the threads to assist in the removal.
Straight Fluted Extractor
Spiral Fluted Extractor