Cut a 4x8 sheet of plywood to 36". Put the good side of the plywood down on the table. Measure across three 23" lengths and up 18" to mark the center of the three holes.
Place a nail at the center marks for all three circles. Attach a string to the nail and the other end to a pencil. Measure out 10" with the rope. Then make a circle using the rope. This will give you an opening of 20". Do this for all three circles.
Note: You may adjust the size of the circle to make it easier or more difficult to "complete" a pass.
Drill a pilot hole near the edge of each circle, and use a jigsaw with a narrow blade to cut out all three circles.
Once you've cut out the circles, place angle irons on both the top and bottom edges of the plywood. These will help to hang the target. The angle irons are long brackets with holes throughout, and they're available at most home improvement stores. Place them horizontally along the top and bottom edges. You'll need several angle irons to cover the entire 8' length. Drill several 1/4" holes across the length of the angle irons and secure them to the wood with 1-1/2" bolts, washers and nuts.
Once the angle irons are attached, run two threading rods down each side of the plywood. The threading rods will be bent and used to hook over the crossbar. Before inserting the rods through the angle irons, bend them into shape.
Screw one washer and nut to the middle of the threading rod, then place the bottom of the threading rod through the holes of the angle iron. Once the threading rod is below the bottom angle iron, screw another washer and nut onto the rod. You now need to spin the threading rod to get it to go all the way through the angle irons. You can do this by hand or use an old carpenter's trick. Place the bottom end of the rod into an empty drill head, spin the drill backward slowly and the rod will come through the angle irons. Once it's fully through, tighten the washers and nuts to secure the threading rod to the angle irons.
A good way to do this is by using an old hose. Take a utility knife and cut the metal end off the hose, then slide the rod into it. Bend the rod while inside the hose -- this will make it easier to grip and protect your hands. After the rod is bent, use a utility knife to slice the hose open around the hook. Cut off the hose and use a second piece to do the same for the second threading rod.
Prime and paint the front of the throwing targets as you like. Try painting your targets three different colors as we did. This is not only decorative, but it will also allow the kids to create games while practicing.