shaft through suitable roller bearings or the like this drum is held stationary by weights or magnets not shown and further constructed of three or more segments which permit the diameter thereof to be varied and therefore the adjustment of the length of each loop of yarn stored thereon the drum 26 is also formed with a frusto conical section 28 which is arranged with respect to the arm so that upon energization of the motor 18 the arm 22 rotates about the drum 26 to wind loops of weft yarn thereonto the frusto conical section 28 serves to induce the newly wound on weft yarn loops to slide along the drum toward a section 30 thereof which tapers slightly in a direction away from section 28 during operation of the loom located adjacent the periphery of the drum is a retaining device generally denoted by the numeral 32 as shown this device includes an actuator 34 and a plunger 36 which is normally projected in a manner to be received in a recess 38 formed in the slightly tapered section 30 of the drum and thus prevent any of the loops of yarn y wound on the drum 26 from being removed therefrom the plunger 36 is arranged to project through an aperture 40 formed in a cover 42 on which a weft yarn sensor 44 is mounted upon energization of the actuator 34 the plunger 36 is retracted into the aperture formed in the cover 42 in this arrangement the weft yarn sensor 44 is arranged to emit a beam of light.