Before their use on the loom, wrap and filling yarns must be prepared for weaving. In preparation for weaving, each wrap end (yarn) must be threaded through its own drop wire, heddle eye, and reed dent. The Drop wire is a device that will stop the loom if an end should break, the heddle eye is the opening in a heddle that carries the yarn, and the reed comb like device that will push each filling yarn close against the completed fabric.
Placing the wrap yarns on the loom is done either by drawing-in or by tying-in. Heddle wires are held in frames called harnesses. The number of harnesses required for the loom is determined by the weave.