5 Worst Impact Wrench Mistakes

1. Over tightening fixings

This is probably the most common mistake people make when using an impact wrench for the first time. In an effort to ensure that the nut or bolt is adequately tightened, they stretch or strip the threads. Strictly speaking, an impact wrench is designed to loosen fixings rather than tighten them. It can also be handy for the fitting & removal of nuts or bolts to save time but, as you will discover, this can lead to another mistake.

Even if there is no damage to the threads, excessive tightening of nuts and bolts can cause problems.

Most of us will have experienced the scenario of struggling to remove a wheel nut (lug nut) to change a tyre that’s been fitted by a mechanic with an impact wrench. If tightened to the manufacturers specifications, the nuts can usually be removed by hand, using the wrench provided.

To stop nuts being over tightened, some of the more expensive units now have built-in torque limiting devices. This method is not suitable for tightening to a precise torque setting but it's ok for tightening fixings with a broad tolerance on the torque setting, General fixtures, like lightweight paneling for example, can be tightened with a torque-limited wrench because they are not safety critical. On the other hand, a critical component like an engine bolt or chassis fixing must be tightened to the correct torque setting by hand, using a torque wrench.

Tightening a nut or bolt beyond the specified torque value could result in stretching, which could lead to the fixing losing tension or failing. Stripping the thread, however, is a more common event and one that most of us will have had to deal with at some time. Repairing a stripped thread can be a costly task, in terms of both time and money. It is important to note that most manufacturers quote torque figures for clean, dry threads. Always check with an experienced professional if your threads are not clean and dry and you are tightening a safety critical fixing.

In conclusion, the best course of action is to use an impact wrench for loosening and removing/refitting nuts and bolts, and a torque wrench for tightening them to the manufacturer’s specified torque.

2. Thread damage

Damaging threads is usually caused by cross-threading the nut or bolt prior to tightening it with an impact wrench. The best way to avoid this is to ensure the nut or bolt it correctly threaded by hand before using the impact wrench. Your hands are much more sensitive than a torque-limited impact wrench so use them first. Soft metals, such as brass, are more easily damaged by cross threading than harder metals so this method is particularly useful when working with these materials. If a fixing is too tight to thread by hand it might need modifying or cleaning with an appropriate tool.

A useful tip is to use helicoils in situations where a nut or bolt is regularly fitted and removed from a soft metal or is under high load.

3. Using the wrong sockets and damaging fixings

Many inexperienced people use regular sockets with an impact wrench, which inevitably leads to them slipping. Ordinary sockets are not designed to be used with a cyclic load so tend to wear quickly and become oversized, causing them to slip on the fixing. Impact wrench sockets are heavy duty and grip across the flats (for hex fixings) to prevent them wearing, damaging the fixing and slipping.

4. Buying an impact wrench that is oversized or undersized for the task

Another common mistake is buying the wrong size impact wrench. If the tool is too large, it may be difficult and tiring to use but if it's too small, it might not be up to the task so it can be hard to decide what size to buy. One way to think about it, is to consider what size of hand socket wrench you'd use for the job, as mentioned in my "Beginners Guide to the Impact Wrench". For example, you wouldn’t use a 1-Inch drive hand wrench to release a 3/8-Inch nut, and the same applies to an impact wrench.

Next, consider where you will be using the impact wrench and how long for. For example, for use in tight spaces an air impact wrench is smaller and has a better power-to-weight ratio than an electric one making the more suitable choice. This is why electric or cordless models are usually better for home use because you don't need a compressor and airline, whereas air is preferred by professional garages where they have the equipment on site.

From a more technical perspective, if you know the torque required to release your largest fixing, then you can check this against the torque rating of the impact wrench. As long as it has a rating greater than the required torque, you shouldn’t have any problems. If the fixing has corroded or fretted however, you may need more torque to release it than the value it was tightened to. To overcome this problem, as a general rule, factor in a 20-30% higher torque rating than you originally estimated.

5. Purchasing the wrong model of impact wrench

Similarly to mistake number 4, people often buy the wrong type of impact wrench. Depending on the task, each type has its own positive and negative features. Air tools have the optimum power-to-weight and power-to-volume ratios and so are preferred by race mechanics and garage workers. For occasional home use, electric tools are a good option as they have a good power to weight ratio and are generally less expensive. Cordless tools are the only portable option but tend to be larger, heavier and more expensive than air or electric units. Additional features such as a torque limiter, battery indicator or extended warranty should also be carefully considered to ensure you get the right tool for the job.

To help you avoid these mistakes, our impact wrench reviews are written to guide you through the process from beginning to end. If you are still uncertain which model is best for your application after reading the reviews, ask your question in the comments below the reviews and we will do our best to assist you. Otherwise, please contact us directly and we will try to answer your query to the best of our knowledge.