and secured by attachment pieces 31 the thread guide tubes 25 may have different inside widths a two opposing thread guide tubes 25 in each case having the same inside width a in an advantageous embodiment this means that two of the respective thread guide tubes 25 are matched to a specific yarn diameter d with regard to their inside width a and can simultaneously be positioned in the yarn inlet opening 2 or in the yarn outlet opening 3 of the yarn treatment chamber 21 the attachment piece 31 is matched with regard to its dimension to a receiver 32 shown schematically in fig5 and shown in section in fig1 a and arranged in the region of the yarn inlet opening 2 or the yarn outlet opening 3 of the yarn treatment chamber 21 in such a way that the thread guide tubes 25 can be installed in the receiver 32 without problems and removed again as already indicated above the receiving element 26 shown in fig2 is mounted in the installed state by a central opening 27 in the manner of a revolver magazine in an advantageous embodiment in other words the receiving element 26 is rotatably mounted on a bearing point 34 and if necessary can be manually or mechanically positioned in such a way that at least one of the thread guide tubes 25 mounted in the sliding guide bodies 30 can be inserted into the receiver 32 of the yarn inlet opening 2 and or into the receiver 32 of the yarn outlet opening 3 of the yarn treatment chamber 21 the receiving element arranged in the region of the yarn inlet opening.