NCs are getting older and in many cases the upper spring isolators are in rough shape and not ideal to reuse when doing a suspension swap. These isolators are a single piece of rubber that not only cushions the top of the spring, but also extend down and function as a dust boot as well. You may want to consider changing these out when doing a spring/shock change.

For the front springs on an NC. Mazda p/n F151-34-012B. Sold individually, one needed per shock.