Difference in auth key commands?

Shell Programming and Scripting
1

Good morning!

What is the difference between:

ssh-keygen -t rsa

and

ssh-keygen -b 2048 -t rsa?

Thanks
Bigben

2 
ssh-keygen -b 2048 -t rsa?

2048-bit RSA keys

ssh-keygen -t rsa

1024-bit RSA Keys

3

man ssh-keygen