If your current eyecup is glued to the metal threaded insert, then you need the fine pitch insert and eyecup. If the eyecup peels off the metal threaded insert easily, then you only need the replacement eyecup.
If your current eyecup is glued to the metal threaded insert, then you need the fine pitch insert and eyecup. If the eyecup peels off the metal threaded insert easily, then you only need the replacement eyecup.