Abstract: Apparatus for automatically forming a yarn reserve on a wind-up bobbin of a yarn treatment machine, is described in which a slot disc at one end of the bobbin pinches and tears off the yarn prior to causing the yarn to engage a first stationary catching thread guide through which the yarn passes while being wound to form the yarn reserve. However, as the usual reciprocating thread-guide approaches the end of the bobbin, a movable thread-guide element fixed thereto transfers the yarn to a second stationary catching thread-guide. Then, on reversal, the movable-thread-guide element releases the yarn, the second catching thread-guide being positioned so that the yarn then enters the reciprocating thread guide to enable the yarn to be wound up to fill the bobbin in the wind-up range thereof.