be greatest producing the largest fiber diameter for layer 76a with pumps 23b and 23c being progressively less producing medium fiber size for layer 76b and smallest fibers for layer 76c other variations of the filter tube construction are possible with the present meltblowing system and are described below under 34 operation 34 as indicated above the mandrel assembly 11 provides rotating mandrel 13 for forming the meltblown tube and advancing it linearly underneath and parallel to the row of orifices 59 as fibers are deposited and wound thereon as best seen in fig3 and 7 the rotating mandrel 13 comprises an outer shaft 81 an inner shaft 82 and a threaded screw take off shaft 83 secured to and in axial alignment with the inner shaft 82 as at 84 the inner shaft 82 and screw take off 83 rotate as a unit and are journaled to rotate relative to outer shaft 81 by bearing 86 the outer shaft 81 is journaled in outer shaft bearing housing 87 by spaced apart bearings 88 and 89 an end of the outer shaft 81 extends a short distance out of housing 87 and is keyed to pulley 91 the inner shaft 82 extends without interference through the outer.