When it comes to choosing the right spanner for a job, there are a few things to keep in mind.

First, consider the size and shape of the nut or bolt you will be working with. Spanners come in a variety of sizes and shapes, such as open-ended, boxed, and combination. 

Open-ended spanners have a U-shaped jaw on one end and a straight jaw on the other, while boxed spanners have a closed loop on both ends. Combination spanners have one end that is open and the other that is closed.

Next, think about the material of the nut or bolt. Some spanners are made from softer materials, such as aluminum or plastic, and are better suited for working with softer metals or plastics. Other spanners are made from harder materials, such as steel or chrome vanadium, and are better suited for working with harder metals.

It's also worth considering the torque you will be applying. Some spanners have a longer handle which allows you to apply more torque, while others have a shorter handle which allows for more precise control.

Another thing to consider is the type of work you will be doing. Adjustable spanners are a good option for jobs that require a lot of adjustments, while ratcheting spanners are great for jobs that require a lot of tightening and loosening.

Finally, think about the quality of the spanner. A high-quality spanner will last longer and be less likely to break or wear out, saving you money in the long run.

In summary, when choosing the right spanner for a job, consider the size and shape of the nut or bolt, the material, torque you will be applying, the type of work you will be doing and the quality of the spanner.