drum 7 as is well known in the art of a coiling arm 8 and of one of several thread locking elements 9 mounted stationary relative to the drum and spaced around the periphery of the drum 7 the elements 9 may be electromagnetically actuated pins as in the previous embodiments according to this embodiment of the present invention the desired length of weft thread 10 is accumulated on the drum while retained by the locking element 9 and is released from the drum by actuation of the electromagnetic locking element the locking element 9 may be automatically moved axially across the surface of the drum to adjust the length of the weft thread accumulated for insertion into the shed by moving the locking element axially the path length between the locking element 9 and the main blower 4 is adjusted in an additional embodiment not shown several thread locking elements 9 may be provided along a common axial path fig6 illustrates schematically still another alternative embodiment of the invention where the thread locking elements 9 spacially arranged around the drum can be moved separately a predetermined distance in a tangential direction with respect to the drum in this way the path length of the accumulated weft thread may also be adjusted in a similar manner to that of the embodiment of fig5 according to another alternative embodiment illustrated in fig7 the adjustment of the length of the released weft path is achieved when the aforesaid thread locking elements are moved together a predetermined distance in a tangential direction with respect to the drum 7 the movement of the locking elements around the drum for adjusting the weft length can be achieved for instance by means of the device illustrated in.