Device (1) for blowing and stretching a plastic parison (3) for obtaining a container, comprising: a blowing nozzle (4) having a first end (4a) to be applied to an inlet (3a) of said parison (3), said first end (4a) emerging in a controlled-contamination environment (5) wherein said parison (3) is blown; a stretching rod (2); means for injecting mid and high pressure air in said parison (3); a non-magnetic tube (7) secured to a second end (4b) of the blowing nozzle (4) and defining a chamber (8) for housing, at least partially, the stretching rod (2), said chamber (8) being tight-sealed relative to a contaminated area (22) from which said controlled-contamination environment (5) is isolated; a first magnet arrangement (9) and a second magnet arrangement (10) coupled together, said first magnet arrangement (9) being located outside said chamber (8) and said second magnet arrangement (10) being integral to said stretching rod (2) and located within said chamber (8).