It is always a good idea to replace prop nuts and tab washers when replacing a prop. Nyloc nuts (nuts with a nylon insert) are ideal for prop installations. They stand up to extreme conditions and resist vibration to secure the prop. In repeated use, the nylon will break down and lose the ability lock the nut in place. It is good practice and recommended to replace these locking nuts each time you replace the prop. Mercury offers prop nuts packaged with two tab washers (where applicable) for the next propeller change. The kits are handy to have zip-tied to your spare prop or in the tool kit. Key Features Locknut secures prop under extreme conditions and stands up to vibration Included locking tabs provide added security (except 16147Q and 16146Qthat use cotter pins not included) Ideal as a spare for unexpected prop changes .