Note: you can use them with any 1:10 scale model - they're 12 mm hexes - not only tamiya FF03. They are wider than stock (4 or sometimes 5mm) giving you wider stance - no need to use offset on the wheels.
They are meant for my short course truck stock plastic hex wheel adapter. So, they are not necessary for FF03 only. These are more durable and lighter than plastic one. Be sure to get one of these if yours are plastic. You definitely won't regret.