What’s the difference between a liner and a shader needle?

The difference lies in the way in which needles are assembled. For example, in a 3-tip liner the needles are welded close to one another, thus enabling the professional to trace a neat, clean line. In a 3-tip shader, on the other hand, distance is maintained between needles, which are then welded, thus creating less neat lines, i.e. shading.
Among 1-tip needles, Pure needles are indicated for lines and any other dimensions can be used for shades or other techniques. The flexibility and smoothness of the needle play an important role in shading.