"Files of type:" filters the files that you will see in the folder that is open. You can also type in a filter where it says, "File name". The filter that would work for what you want is *CAT* (enter). This will show any file with "CAT" in it, if you just want parts: *part, the asterist at the end is not needed. This is not the way I search, I usually know part of the number or name of the file, which reduces the number of files shown. You have many option with the use of wild cards (*). If you search with *4*7*part it will show all files with "4" and "7" and "part".