Sharon, did you buy it from Rudy?
If you bought it from Rudy it will fit. The original "rope to cable", idea has been updated to rope only. The new lines are strong abrasion resistant and not affected by water. Not all 25 O'days have the same set up to the centerboard. I will try to explain the one I know. The center board is on a pivot. The pivot is about 12 to 16 inches back from the front of the center board trunk (housing). I would suggest a quick inspection of the pivot while on the travel-lift.OK back to the center-board pennant...The center board is about 5' long. The centerboard penenant ( the rope you are talking about) is connected to the trailing ( the aft portion, the back side) of the centerboard about 8 to 10 " above the bottom of the board. The connection I know of, is a stainless steel strap in a "U" shape that is bolted through the trailing edge of the centerboard about 8 to 10 " above the bottom of the board when it is down. The "U" shaped piece is about 3 to 4" long and connected with a 1/4 to 5/16" s.s.bolt and nut with nylon.The connection from here has many variations. The pennant I changed, I used a shackle to connect a 1/4" polyester pennant to the stainless steel strap.I think your 1/2" line is too heavy. The board is light and the 1/4" polyester line would be fine. I did splice a loop in the centerboard side of the pennant.I hope this helped. I did mine in the water under the boat.r.w.landau