According to the Park Tool website, the FR-5G will work on the Shimano cassette lockring, however I can't seem to get it to fit. The splines line up correctly, but it looks like the diameter of the tool is just a little bit too large to fit inside the lockring. I have a 105 cassette - it's like a 2010, so I guess it's a 5700?

Anyone else have any experience with this? Do I have the wrong tool? Is there anything I can do to make it work (I haven't tried the "get a bigger hammer" approach).