Although the open example specified 0666, the actual file permissions are calculated with a mask that may restrict access further.

The mask is called the umask and there is one for each user.

The umask can be inspected and/or changed at the prompt:

        $ umask
          0022  (output example of the umask command)
     

Actual file permissions are calculated like this:

        actual_permissions = specified_permissions & ~umask