to become juxtaposed with the segment 15a 2 the same is true with respect to the segment 15b 1 vis a vis the segment 15b 2 moreover even though that is not shown in the drawing there could be provided two or more other segments which could be referred to as segments 15a 0 and 15b 0 for the sake of consistency even though they are not shown in the drawing that would then be juxtaposed with the segments 15a 2 and 15b 2 respectively etc the 34 folded back 34 segment or segments can be of one piece with the main ribbon sections 11a and 11b or they can be discrete auxiliary ribbon sections advantageously all of the segments 15a 1 to 15b n have substantially equal lengths but that is not critical as a matter of fact in some cases it may be even preferred to make them of unequal lengths even in that case though the associated ones of the segments 15a 1 to 15b n that is those that are directly juxtaposed with one another such as for example 15a 4 and 15b 4 or for that matter 15a 1 and 15a 2 do have substantially equal lengths for the sake of completeness it is to be mentioned that the indentations 16 and 17 are offset like in the above cited patent longitudinally from one another on the opposite edges of the ribbons 11a and 11b so that a narrow neck portion 18 is formed between each pair of indentations 16 and 17 that has its narrowest portion.