The refined ‘Sweet Spot’ (Center Of Mass) of a golf clubhead is about the size of a good old American Dime. If you prefer Lincoln’s coin, that is OK too! Close enough for the golfers I have known over the decades!
The more compassionate ‘Sweet Spot’, for week-enders, might be the size of a quarter.
The beloved hacker might more subjectively make a 50 cent piece work?
However, the hard truth is that the ‘Ballistic Point’ of a golf ball (The Bottom Inside Cheek – BIC) is only the size of the biggest dimple. Now that presents a challenge.