You will need to buy twice as much line as the height of the pole (20' flagpole 40' line)
Please note sizes of line v. pole height are estimates and may vary.
How to Restring your flagpole
Normally flagpole halyards are or should be set up in a way so that the line is one continuous loop, with a square knot securing the ends together. the snaps are then spaced either side of the knot. We do not recommend leaving the ends un-knotted with the snaps secured to them , if one of the ends gets away from you it may slide to the top of the pole and be next to impossible to retrieve. To restring the pole cut the old halyard between the last snap and the top of the pole (DO NOT LOSE THE THE CUT END). Using either a needle and thread or electrical tape butt splice the end of the old line to the end of the new line. If using needle and thread run several stitches from one line to the other at 45 to 90 degree angles, make one wrap of electrical tape around the ends of both lines. If using tape only make a continues series of wraps from one line to the other starting several inches before the end the warps must be tight. Make sure the joint / splice is supple enough to make the bend over the pulley and strong enough that it doesn't fall apart when pulling the line through. Gently pull the old line up and through the pulley and back to the ground. If you feel any resistance bring the splice back down and flex it a few times to loosen it up a bit . Cut the new line free of the old one and the spliced area, tie the two new ends together with a square knot and finish the tails off with several warps of white electrical tape. Measure half the length of the hoist of your flag measure up from the knot in the halyard the same distance and add an inch pinch the line forming a loop Pass the loop through the hoop of the snap and up and over the head of the snap pull back on the standing end of the lines to tighten repeat on the other side of the square knot at the same distance.
REMEMBER DO NOT LOSE EITHER END OF THE HALYARD
