Treat the shaft as the investment piece
A well-fit shaft can stay useful across multiple driver heads. The fitter uses the player's seven-year-old shaft as proof that the shaft has longevity and calls it the engine, while driver heads are the parts that can be replaced more often.
Channel: Club Champion
Watch official source at 5:54Why this context matters
The player has reused the same fit shaft with newer driver heads over several years.