Restore to default user prefix

I deleted the user prefix, how can I restore it to the default?

I know where to but what do I enter into the field.

I currently have web[id] but when i create a mail user:

error

username must be at least 4 characters and a maximun of 32 characters. First one must be a letter.

 

Answered my own question.

For any others that do this check this post.

http://www.howtoforge.com/forums/showthread.php?t=1285&highlight=webid