Grommets are metal eyelets that reinforce hook, rope, or cable holes in fabric or plastic. Kits, available in sewing supply shops, include a setting tap for joining the grommet halves. Hardware stores have kits of heavier grommets for tents and tarpaulins.
Using scissors, cut a hole or an X in the material; make it slightly smaller than the opening of the deep grommet half. Push the end of that half through the hole on the right side of the material; put the end of the shallow half over it on the wrong side. Fit the stud end of the setting tap into the opening of the shallow half, and hammer it to crimp the grommet together.
Before replacing a grommet, patch light fabric with seam tape; use nylon webbing with heat-sealed edges for heavy fabric. Burn grommet holes in nylon patches with a soldering iron.