The Echo CS-400 chainsaw has a 18-20 bar and chain combination, which requires a 0.058 inch (1.5 mm) gauge file for sharpening the chain teeth properly. This size is also referred to as full skip, meaning that it will leave two cutting edges on each tooth when used correctly. It's important to always use the correct file size, otherwise you risk damaging the saw or not getting an optimal cut from your chainsaw blade. Additionally, you should always clean off any dirt or debris before filing to ensure that your results are as accurate as possible!