For 0.4 stones, the first step is to determine whether they are 0.4mm, or 0.4cm, commonly described as 0.4cm stones.0.4mm stones are very small, and can soon be eliminated on their own by drinking plenty of water and urinating.0.4cm stones are generally not serious, and in the vast majority of cases can be eliminated by drinking water, taking stone-eliminating medication, and exercising appropriately. In principle, stones smaller than 0.5cm can be eliminated by themselves. There are also a small number of patients with poor stone removal ability, thin ureter, fear of pain, do not like to drink water, and 0.4cm stones have not been discharged, blocked in the ureter, which may lead to hydronephrosis, renal pus. It is recommended that 0.4cm stones be discharged early after discovery, and if it is difficult to discharge the stones, extracorporeal shock wave can be considered to discharge the stones again afterward.