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Make sure that the 2 posts are standing on a level, flat surface. Then, use a tape measure to measure up the post 18in (46cm) from the ground. Use your pencil to make a mark on one of the flat sides of the post. Using the level, draw a horizontal line through the mark. Draw another line at the same height on the opposite side of the post. Then, continue measuring up the post in 3in (7.6cm) intervals until you've marked 9 lines. Repeat the process on the second vertical post by measuring and marking lines first at 18in (46cm) and then at intervals of 3in (7.6cm) until you have drawn 9 lines. These marks must be completely level and centered or your jump cups won't fit correctly into the posts. When you've finished, the 2 posts should each have 9 lines marked around them at the same heights. " Measure the width of one of the vertical edges of the post and divide by 2 to find the center. The result should be close to 1.5in (3.8cm). Use a pencil to mark an "X" at the center of the lowest line on the post. Then measure the halfway point at the line of the same height on the other side of the post. Make another "X" here. Make sure to be consistent and mark your "X" markings on the same 2 sides of the post. Do this for each of the 9 lines you've drawn on both posts. Repeat this process on the second post as well. Keep in mind that, when marking the center of the 9 lines on the second post, you won't need to re-measure the width of the post, since the 2 posts are the same size. Set a 12 inch (13mm) drill bit in your power drill. Then, position your drill bit against the first of your "X" markings on 1 of the posts. Hold the drill level, and drill straight through the post. Drill slowly for the sake of accuracy, and aim the drill bit for the "X" on the back side of the post. Drill 9 holes: 1 through each set of "X" marks you drew. Then, repeat the process and drill 9 more holes through the second post. As with the first post, hold the point of the drill bit in the center of an "X" mark, keep the bit level, and drill straight through the post. Make sure that the holes you drill through the posts are all on the same 2 sides. None of the drilled holes should be perpendicular to each other.
Mark 9 lines at 3in (7.6cm) intervals up one of the posts. Mark the center of each of the 9 lines on the posts with an "X. Drill holes straight through the 9 sets of "X" marks on both posts.