assemblies 10 on each side of the tufting machine when the tufting machine is in operation only one of the eight gear housing assemblies will be in the yarn advancing position illustrated in fig3 and the remaining seven gear housing assemblies would be in the yarn clamping position illustrated in fig4 when it is desired to switch the yarn being supplied to the associated needle the gear housing assembly 10 in the yarn supplying configuration of fig3 is operated by the application of air pressure to port 43 of air cylinder 42 to disengage yarn 34 and yarn roll 36 from the driven yarn roll 37 and to simultaneously clamp the yarn 34 between the tension bar 51 and weight block 20 the action of the weight block 20 and the clamping action performs two functions that appear to improve the preciseness of the yarn feed 1 to prevent the elasticity of the yarn between the yarn supply and the yarn clamping area 23 to substantially alter the length of yarn that has already passed between the position of the yarn rolls and 2 to prevent the unintended advancement of yarns either by the reciprocating motion of the hollow needle assemblies or by the pneumatic urgings applied to the yarns generally so that they feed freely from the yarn supply to the needles when the yarn being supplied to needles is changed just as the gear housing assembly 10 of the previously supplied yarn is.