Several of the cheaper "kit" lenses offered by Nikon have plastic mounts. While these lenses have great optical quality, a number of us have managed to break of one of more of the platic mounting tabs. I recently replaced the mount after I managed to break off one of these tabs (I was clumsy and dropped my D40x about 6 inches, onto a carpeted surface). The cost of replacement part was around 17 dollars, including shipping. A new lens would have been over 100 dollars. The actual lens that was repaired is the 18-55mm G series zoom. I also have a 55-200mm zoom, and it has the same plastic mount.
Step 1: Order/obtain Replacement Lens Mount
I got mine from Nikon usa for about 17 dollars including shipping. Please take note of the screw, brass plate and chrome mounting post in the left side of the first photo. These are included with the replacement part. I removed these and used the existing ones instead.