Cut four 7-foot pieces of 4-by-4 lumber, and a fifth piece that is 9 feet long.
Cut one end of each 7-foot piece to a 45-degree angle. This will allow these pieces to rest flush on the ground.
Paint or stain the boards if desired.
Insert the uncut ends on the 7-foot boards into two A-frame brackets, with the tip of the cut end facing away from the frame, creating two large V shapes.
Drill holes through the boards, using the bolt holes in the brackets as a guide for hole diameter and placement.
Bolt the boards to the bracket through the holes that you have drilled. You will use 12 mm galvanized bolts that are 5 to 6 inches long, depending on the thickness of the bracket's sides. Each bolt should have a washer threaded onto it before passing it through the frame, and a second washer added before screwing on the nut.
Tighten all nuts with a pair of pliers.
Stand the two A-frames up and insert the 9-foot board into each bracket's third flange, completing the swing frame. You may need a few friends to assist with this step.
Drill holes through the 9-foot board, using the bolt holes in the brackets as a guide.
Bolt the 9-foot board to the brackets.
Screw the swing's mounting eyebolts into the frames top board and hang the swing.