the driver plates 34 of at the same time as the levers 27 are themselves introduced on the pin 39 in a variant embodiment it is pin 39 which may be introduced in the assembly of the actuation elements once the elements are on shaft 24 such engagement on shaft and pin elements 24 and 39 ensures both suitable orientation of the elements a with respect to shaft 24 and to the heddle frames b and perfect positioning of the members constituting each element since the driver disc 34 is connected by the hook 35 to the eccentric 29 which is itself connected to the connecting rod 25 by the bolt 31 it then suffices to engage on the end of the shaft 24 opposite the one supported by roller bearing 41 a cap 42 equipped with longitudinal screws 43 cooperating with corresponding tappings in shaft 24 and to tighten the screws 43 it will be understood that if care has been taken to give the inner ring 30a of the roller bearings 30 an axial thickness slightly greater than that of the assembly formed by each eccentric 29 and its plate 29a adjusting of screws 43 ensures by application of the free edge of the cap 42 against the end element a or an appropriate bearing washer the efficient.