The 609, 709 & 811 will all fit the same machine as far as locking system's go. The 811 is the biggest backhoe attachment made by Bobcat in that line. As far as I know. I know the 811 will fit a S185, not sure about the S205? Have you looked to see if it has a place for the stabilizer brackets on the side? If it does, then the 811 should work on it.