This option is located at: Reader -> Setup -> Settings -> Read
The program will download this many message-headers (if available) when the “Get New Posts” and “Get Older Posts” buttons are clicked.
A “message header” contains the basic information about the post: subject, poster, date, etc. On NewzToolz‘s Reader window, you see a list of message-headers, and files which are comprised of two or more message-headers. When you click on a plain message-header, the program downloads the entire post.
A newsgroup can contain zero posts or millions. When you click the “Get New Posts” button, how many message-headers do you want the program to download? At first thought, it seems like you would want to see them all. However, it takes time for message-headers to download, so normally, people will download them in small batches, but it is a matter of taste.
We say “if available” above because there may be less message-headers in the group than in your batch size. If you have this number set to 300, and the sever only has 200 message-headers, then only 200 will be downloaded.