referring firstly to fig1 and 2 , shown therein are two control needles 1 and two hooks 2a and 2b . the control needles 1 are mounted in a needle board 3 and a needle rake 4 . the control needles are controlled in the usual manner by means of a card prism or needle control mechanism diagrammatically indicated at 5 . pulses from the card prism 5 are transmitted to the hooks 2a and 2b by angular projections 6 which are disposed on the control needles 1 . the hooks 2a and 2b are guided between a hook rake 7 and , in their rest position , are supported on a stationary hook bottom member 8 . disposed above the hook rake 7 is a lower set of knives or blades , as indicated at 9 , while above the lower set 9 of blades is an upper set 10 of knives or blades . the purpose of the sets 9 and 10 of blades is to carry hooks which have not been pressed away by the control needles 1 into the upper shed position or correspondingly actuated hooks into the lower shed position . for that purpose , each of the hooks has hook projections or noses 11 and 12 on a leg portion of the hook , with one nose 11 being disposed at the upper end of the hook ( the nose 11 is more clearly visible , for example , in fig3 ), while the other nose on the hook is disposed at a lower position thereon . in the upper shed position , the hooks 2a and 2b are supported with a further hook projection or nose 13 on a set 14 of arresting knives or blades which are disposed below the control needles 1 . the two sets 9 and 10 of blades are arranged so as to move in opposite directions towards and away from each other , but without crossing . the sets of blades each perform a rectilinear vertical movement towards and away from each other . in addition , each blade of at least one of the sets of movable blades , being blades 15 of the upper set 10 in the illustrated embodiments , is arranged for pivotal movement about an imaginary axis a ( see fig4 ) which extends in the longitudinal direction of the respective blades . the loom further includes a pivoting means 16 for producing simultaneous and parallel pivotal movement of the blades of the set 10 . dealing now in greater detail with the pivotal means 16 , and referring also therefore to fig3 the blade box or housing associated with the upper set 10 of blades has a frame member or structure as indicated at 17 , in which there are provided apertures 18 of substantially triangular configuration . the blades 15 of the upper set 10 are pivotal in the apertures 18 between the position shown in fig3 and the position shown in fig4 . for that purpose , each of the blades 15 carries a fixed projection 20a at its lower end , each said projection 20a being connected to a slide track 23 by way of a pivot 21 and an actuating rod 22 . it will be noted from fig3 and 4 that the upper end portion of each blade 15 has a recess 19 corresponding to and adapted to cooperate with the end portion of the nose 11 of the associated hook . upon lifting movement of the upper set 10 of blades by means of a lifting arrangement ( not shown ), the operational effect of the slide guide means 23 and the pivoting means 16 is to cause the blades 15 of the upper set 10 to pivot from the lower limit position of the upper blade set 10 , as shown in fig4 into the position shown in fig3 when the arrangement has covered half the distance of the slide guide means 23 . in the upper limit position of the blade set 10 , the blades are then pivoted back into the initial position shown in fig4 by virtue of the configuration of the slide guide means 23 . those hooks 2a and 2b which are engaged by the respective blades 15 are deflected or pivoted during the upward and downward movement of the upper set 10 of blades , as can be seen from fig1 . this deflection movement is such that the lower noses 12 on the hooks move past the blades of the lower set 9 of blades , and are therefore not engaged by the lower blades 9 . the upper blades 15 are therefore used as a lever arm in such a way that , upon pivotal movement of the blades 15 , such a force is applied to the hook carried thereon that the hook is bent away to such an extent that the respective other nose on the hook passes out of the path of engagement of the other set of blades . referring still to fig3 and 4 , each hook may also carry a projection or cam member as shown at 20 . in the illustrated embodiment , for the sake of improved clarity of the drawing , only the hook 2b is shown as carrying such a projection 20 . it will be clearly seen from both fig3 and 4 that the projection 20 on the hook is arranged at a spacing from the hook nose 11 , which corresponds at least to the dimension of the pivotal blade 15 , as measured in the longitudinal direction of the respective hook . in practice , the space between the projection 20 and the hook nose 11 is somewhat larger than the above - mentioned dimension of the respective pivotal blade 15 , so that there is an additional small space between the lower end of the blade 15 and the projection 20 , in order to permit the hook nose 11 to be moved into a position of support on the blade 15 , without hindrance . when the blade 15 is in the pivoted position as shown in fig3 the projection 20 on each hook ensures that , in the event of the machine coming to an abrupt halt , the hook supported on the blade 15 cannot continue to move further upwardly so that the nose 11 of the respective hook could come away from the respective blade 15 , which could result in defects in the article being produced on the loom when the loom is restarted . reference will now be made to fig5 which shows another embodiment of the means for preventing the hooks from jumping off the blades in the event of an abrupt stoppage in operation of the machine . it will be appreciated that the embodiment shown in fig5 operates in substantially the same manner as the embodiment shown in fig3 and 4 in regard to the action of the projection 20 , insofar as the blade indicated at 15a in fig5 has a projection portion or cam member 24 while the hook 2c has a recess 25 adapted to receive the cam portion 24 as clearly visible in fig5 thereby to produce interengagement between the blade 15a and the hook 2c , in the same manner as the cooperation between the blade 15 and the projection 20 in fig3 and 4 . it will be appreciated that the constructions described above with reference to the drawing are only preferred embodiments of the invention , and that various other modifications and alterations may be made without thereby departing from the scope and spirit of the present invention .