On a lot of vehicles made during the past 20 years, the manufacturer used a two-piece lug nut that has a chrome cap over the steel lug nut. On the new car lot, these look good on a nice set of alloy wheels. But, in as little as three years, the lug nuts could swell and make removal difficult.
The problem with these lug nuts is that water and salt gets between the nut and cap. The resulting corrosion causes the cap to swell and change the outer diameter of the nut. For the driver, this often means the lug wrench in the trunk will no longer fit when they need to change a tire by the side of the road.
For a technician, it could mean extra time and tools to remove the lug nut. It is not impossible, but the key is to identify the problem before you make it worse. The rookie mistake is to grab the next larger size socket and use an impact wrench. This method can dislodge the chrome cap, but it can also round off the harder nut under it. Senior technicians know that not too many lug nuts come in 18mm, 20mm or 22mm sizes, so if they feel resistance when trying to get the socket over a lug nut, they put down the impact before they make it worse. The impact is a great time saver, but it lacks the feel and overall torque of a good breaker bar. A good technician also knows the feel of a properly engaged nut and socket with a breaker bar better than an electric or pneumatic impact.
Some technicians have purchased over-sized sockets in 19.5mm and 21.5mm size to remove swelled lug nuts. Some technicians have had luck with 12-point sockets in 11/16” and 3/4” sizes. Using these slightly oversized sockets involves hammering the socket over the swelled lug nut and using a breaker bar. Unfortunately, sometimes the lug nut then becomes permanently lodged in the socket and won’t come out.
The worst-case scenario is that a previous technician damaged the lug nuts with his impact and now you have to deal with it. In these cases, a drill bit or rotary broach bit might be your only solution.