This LED string light holder is meant to replace zip-tying string lights to your wrought iron fence. Pull the plastic top off each of the upright supports and insert this replacement into the same space. The LED string light wire fits into the groove and can hold itself in place, but there is also a small channel that fits 1.5mm zip ties to go around the wire for added security. The inner diameter of the cutout is 6.5mm and may need to be adjusted for your particular brand of lights.