triggered the arrest of the roving 15 so that it does not hinder the run of the rovings 15 this can be done manually or can be performed automatically by a yarn setting carriage 40 however when a yarn break occurs at anyone of the two spinning units 10 of the spinning units pair 50 which is supplied each with a roving 15 from the same bobbin 26 the respective yarn break sensor 24 senses this and excites an electromagnet 33 of the stopping device 25 an anchor 34 associated with electromagnet 33 holds the bridge 30 and thereby the shells 29 normally in the position shown in fig1 as long as no yarn breaks exist at these two spinning units 10 in this normal position the shells 29 have no influence on the rovings 15 this is due to the fact that the anchor 34 holds a pin 36 provided at the bridge 30 in the position shown in fig1 wherein the two shells 29 are at a distance from the clamping line of the two feed roller pairs 12 if a yarn break occurs at any one of these two spinning units 10 the electromagnet 33 is excited and attacts its anchor 34 which releases the pin 36 both shells 29 thereby become entrained by their friction with the rotating lower roller 27 in the direction of arrow a these shells then reach.