Mercury -
Here was my process for getting it to fit:
1. Remove old bezel, and insert from bezel (be careful not to lose the spring and pin located at 12:00 in the case (almost lost mine the first time)
2. Check the fit of the insert to the crystal. The bezel insert fit too tight onto my crystal, it was really hard to rotate the insert once it was on the crystal, so I got out some 1000 grit sandpaper and sanded the inner circle of the insert until it would rotate easily around the crystal.
3. I used 2 part epoxy to glue the Insert to the Bezel (mine did not quite snap in as an original bezel and insert would). Once glued into position, I set the bezel and insert assembly onto a desk, then placed a glass ramekin (or small glass cup) and the insert and placed several heavy books on the ramekin while the epoxy dried.
4. After an hour or so, I put the bezel and insert onto the watch, vioala - perfect fit....
If there is a better way to do this, I am all ears, er...ummm...well, eyes since we're on a forum and all