in fig1 the tubular portion represents a tubular center piece 10 of the finished tubular body when a second end piece 11 is formed as will be described hereinafter with reference to fig5 when the mandrel 2 a continues to move in the direction of arrow p as shown in fig3 the recess 8 passes by the die 4 as a result the annular gap 7 between the mandrel 2 a and the die 4 increases so that more material 3 is able to flow through the annular gap 7 this causes an increase in the wall thickness of the tubular center piece 10 the flow of material 3 causes an increase of the wall thickness in an outer region but not in the inner region of the center piece 10 fig4 shows the state when the recess 8 has passed the die 4 and the annular gap 7 is smaller again in this case the wall thickness of the center piece 10 decreases material 3 flows past the recess 8 so as to enable the mandrel 2 a to retract again without interference from the recess 8 of the mandrel 2 a this is effected because the recess 8 has already moved past the die 4 in the end position shown in fig4 so that the undercut formed by the recess 8 is not filled with material 3 after the tubular center piece 10 has been formed together with the first end piece 9 in one and the same forming tool 1 a third production step is executed to form a second end piece 11 as shown.