umask permissions that result in no change

Question

I am having a really hard time understanding how umask works.

How is something that is 666 masked with 001 still 666 ?

Answer 1

A umask value of 001 says that it is preventing the creation of files with other executable permissions. (Actually not preventing the creation, as preventing the executable-permissions).

A 666 mode in an open statement only permits user+group+other for read and write permissions. So the umask has no effect on that.

However umask does not affect chmod.