Floyd Rose Tremolo Arm

RT-C Retro-Tremolo Arm System for Floyd Rose Tremolo, Black

This arm includes the mount that screws into the bridge.  Just unscrew the old mount, screw in the new one, and the arm fits perfectly.  You can try to use it with the old mount, and sometimes it will work, but if it doesn't fit well, swap out the mounts and it'll be just the way you wanted it to be.