If you are changing from original parts (8-5500, 19-5500) to new series parts (8N-5500, 19M-550G), it is NECESSARY to change BOTH the main gear and the pinion gear.
If one or the other requires replacement due to wear, it is strongly recommended to change both the main gear and the pinion gear, even if both are the newer type. The wear on one part usually equates to equal wear of the other part.
Please match your part to the image above to make sure you are ordering the correct part for your version of the 5500ss reel. This pinion gear has been modified to fit the 5500ss reel.