of the bit clamps described herein may be of any desired cross sections extend downwardly from pistons 92 which serve as bit clamp carriers the pistons 92 are housed within cylinder block 94 above which is located pneumatic pressure chamber 96 cover plates 97 and 98 complete the wall structure for this chamber a lifter bar foot member 100 is secured to the cover plate 98 and a drive bar 102 provides the drive for reciprocating vertically the entire yarn clamping means 230 the yarn clamping structure 230 of fig4 may be utilized by driving the unit into and out of a clamping position by means of one or more drive bars 102 operating from cam 52 fig1 alternately the structure 230 may be mounted to the main frame of the machine and the desired motion of the bit clamps 90 and pistons 92 produced entirely by pneumatic means i e programming of pneumatic pressure including positive and negative in chamber 96 with reference to fig5 another design of yarn clamping means 330 is shown a wedge shaped member 110 constructed of spring steel or other suitable material is positioned between cover plate 112 and a bit clamp body member 114 a bit clamp carrier bar 116 and a retainer plate 118 are secured by means of bolt member 120 bit clamp body 114 has a guide slot 122 through which the bolt member 120 extends with tolerances such as to permit the biasing effect of the wedge shaped member 110 to be effective against bit clamp body member 114 the bit clamps 124 are shown integral with the bit clamp body 114 a lifter plate 126 is secured to the.