Selvage rods are a guide to help keep the edges of the piece straight and parallel.
You don`t actually pull on them, and they don`t stretch the work. Some people do find them helpful for evenness, while others feel they don`t need them.
These ones are a pair of 1/4" cold-rolled steel rods. Each rod is held by 3 screw eyes - at the top, middle, and bottom of the loom. Each end has a hitch pin clip through a hole, just beyond the top or bottom screw eye. The two middle screw eyes are on little blocks attached to the side bars of the frame. These provide more alignment with the ends of the rods.
The rods go right next to the left and right edge warp strands. The wefts would go around both rod and warp together. When the work piece is ready to come off the loom, one hitch pin clip on the end of each rod is removed, and the rods can slide out.
If you want to make a narrower piece (leaving some of the pegs unwarped), you can place one or both rods next to your outermost pegs, and just tie them to the screw eyes with a length of string or cord.
If you are making a shorter piece (adjusting the peg bars to be closer to each other), the rods will just extend beyond the peg bars.
There`s no extra shipping charge when the rods are added to a loom order.