There is none. "Common" means "same for both" or "same for all".
A single item has nothing common, and a single number has no common factors.
There's nothing that's "same for both" until you have two different numbers.
The GCF is 120.
Since 120 is a factor of 360, it is automatically the GCF.
The GCF of 40 and 120 is 40.Since 40 is a factor of 120, it is automatically the GCF.
The GCF is 120.
The GCF is: 120
The GCF is 6.
The GCF is 4.
The GCF is 60.
The GCF is 12.
The GCF is 60.
The GCF is 20.
The GCF is: 8