stationary and a movable clamping jaw 1 and 2 respectively the stationary clamping jaw 1 is secured through a rubber block 3 to a projecting part 5 of a housing 4 to be mounted stationary e g on the frame of a weaving machine the movable clamping jaw 2 is secured to the one end of a lever 6 preferably made from a light material such as aluminum which is pivotally connected at its other end to the housing 4 the pivot connection is constituted by a leaf spring 7 which is somewhat biased namely so that the spring tends to rotate the lever clockwise as seen in the drawing an electric coil indicated with the reference number 8 is preferably coiled to the shape of a flat spiral and is received in a bridge piece 9 preferably made of plastic extending over the housing 4 and secured thereto the lever 6 extends below the bridge piece 9 and comprises at the position of the coil 8 a disc 10 e g of aluminum which is suitable for induction therein of eddy currents when a current pulse is sent through the coil 8 in the open position of the yarn clamp shown in the drawing the lever 6 with the disc 10 is kept by the biased spring 7 against the coil 8 at its lower side the lever 6 supports a second disc or block 11 of ferromagnetic material which cooperates with the armature 13 of an electromagnet 12 mounted in the housing 4 a current pulse supplied to the coil 8 results in that a large downwardly directed acceleration.