TRy this steps. It works in NX 4, 6, 7.5 & hopefully it will work in higher versions also.
1. Make Helix using "insert ---> curve ---> Helix.
2. Key in the values/parameters in as per your requirment.
3. Make a sketch(Circle) in XZ plane.
4. Use the command Swept(Insert--->Sweep--->Swept).
5. Insert plane constraining it parallel to XY plane & select end point of Helix.\
6. Do the same as point 5 at other end.
7. Use the Trim Body Command(Insert--->Trim--->Trim Body) to trim the spring at end using the plane craeted in point 5.
8. Do same as point 7 at other end.
You can use GC toolkit to develop any sort of gears or springs without complex modeling.