vikingvictory, the insert you use will be determined by the size arrow you shoot. A local pro shop can help you determine the arrow that is best for your set up. The only other choice you may have in the way of inserts is using a carbon or aluminum insert. If you are going to hunt with these arrows, I would sugest aluminum inserts.
The nock inserts you refer to are really called bushings. Bushings for the arrow will come with them, like inserts, they are specific to the size of arrow.
If you don`t get any help from a local archery shop, you will be able to get more info here.
Hope this helps, Good Luck!