Flagpole halyards are typically rigged so that the rope line forms a continuous loop. A square knot (also known as a reef knot) is used to secure the ends together, and the snaps are spaced at either side of the knot. You can usually restring a flagpole from the ground, unless the line has broken so high that you can't reach the end. Avoid a few common mistakes, to have your flag flying again in no time.
Cut the old halyard at a point between the top of the pole and the last snap. Firmly grasp the cut ends so you don’t lose them.
Splice the end of the old halyard to one end of your new line. You may use a needle and thread or electrical tape to accomplish this. Begin by butting the ends of the lines together, but avoid overlapping them. If you decide to use a needle and thread, make a few angled stitches from one line to the other and back. Secure with a single wrap of white electrical tape to cover the ends of both lines completely. If you prefer to forgo the needle and thread, tightly wrap electrical tape several inches from one side of the splice and continue wrapping for several inches beyond the other side of the splice.
Gently pull on the old halyard until it goes it through the pulley and comes back to the ground. The splice you created needs to be strong, but flexible enough to be bent over the pulley. If it is not supple, bring the line down again and flex the splice back and forth to loosen it before sending it back up.
Separate the new line from the old halyard (including the spliced section) using a knife or scissors. Tie the ends of the new line together using a square knot and wrap the ends with electrical tape to finish them.
Measure a distance from the knot in the line that equals half the length of the hoist of your flag plus one inch. Form a loop at this point by pinching the line.
Pass the loop that you’ve created through the hoop of the snap. Then, pass the loop over the snap head and tighten by pulling on the standing end of the lines. Repeat this procedure at the other side of the square knot using the same measurement.
Monitor your flagpole restringing efforts for a couple of days to make sure your knots are holding up.
Do not let go of either end of the rope after you cut the old halyard, or leave the ends of your new line secured to the snaps without knots. You could end up with the ends out of reach. If you are restringing a flagpole due to a break in the line that you cannot reach, you may need to have it restrung by a professional.