show the module 2 a u2032 in conjunction with a further modified adapter 12 u2032 a which except for a positioning rib 33 a projecting from the contact face 49 fully corresponds to the construction of the adapter 12 u2032 shown in fig1 and 14 the rib 33 a corresponds essentially to the positioning web 33 of the adapter 12 b according to fig2 8 or 9 and is provided for securing the module 2 a u2032 to the carrier bar 1 u2032 in accordance with fig2 fig1 and 18 show a module 2 b u2032 having a further modified adapter 12 u2032 b the adapter 12 u2032 b differs from the adapter 12 u2032 according to fig1 and 14 by its two pin like projections 25 u2032 26 u2032 which rise from the planar surface 49 and which correspond approximately to the pins or projections 25 26 of the adapter 12 shown in fig6 the adapter 12 u2032 b is to be coupled with a carrier bar 1 according to fig1 which has orienting openings 27 28 in case the rib 47 and the t shaped groove 48 are arranged centrally on the adapter 12 u2032 or the base body 3 u2032.