A stem (1) for a two-way valve has a main body (10) outer face that is substantially cylindrical about a main axis, with (i) a first tubular wall (11) closed at its lower end by a first bottom wall (13) and open at its upper end (111), defining a central channel (113); (ii) a second tubular wall (12), concentric with the first tubular wall (11) and partially surrounding it, closed at its lower end (122) by a second bottom wall (14) and open at its upper end (121), defining an annular channel (123) around the central channel (113), one or more through-holes (124) bringing the inside of the annular channel (123) in contact with the cylindrical outer face of the main body (10); and (iii) a tubular insert (20) dimensioned so as to be able to be inserted into the annular channel (123).