In other words, it is the process of printing the actual separations for the screens, that will produce how large or small the halftone will print on the shirts. That number 34.6 will be the value for the lpi frequency (lines per inch) which needs to be set up in the separation set up in the output sub menu of the print dialog window in Illustrator. The screen printing company must take the thread count of the mash (and just for an example we will use 156 mesh) and divide that number by 4.5 (personally I prefer 4.73 but the number 4.5 is a good starting point), which will then give us the number 34.6.

There is only one way to avoid this Moire pattern in the final screen-print.

In this image, you will see a moire pattern on the left side which is what the half tone printed with that undesirable pattern would look like and the right side of the image is what you would want the printed halftone to look like on the shirts. The thread count of the screen mesh (threads per inch) can interfere with the half tone pattern and create something what is called a moire pattern.

The main reason it is done this way is because the screen mesh used for the screen-printing. The screen printing company must follow a certain formula for producing and printing half tones successfully. Although it is possible to visually create the actual half-tone dots in the artwork file itself for screen printing, as posted in the answer from It is seriously frowned upon and not recommended.

Adobe photoshop elements 5.0 half tone