Dot matrix printers offer the lowest resolution of all available printers. Although dot matrix printer manufacturers claim resolutions as high as 360 dots per inch, the real resolution of most is only 60 dots per inch. Higher resolutions are simulated by overlapping consecutive dots. The reason that the true resolution is only 60 dots per inch is because the width of each dot is approximately 1/60th of an inch (16 mils). In order to print readable barcodes on a dot matrix printer, the Narrow Bar Width must never be less than the width of a printer dot as it is impossible for a dot matrix printer to print a line narrower than the width of a single dot. The larger the value that you choose for the Narrow Bar Width (within the allowable range for a specific symbology), the more readable your barcodes will be.
When you set up the Windows printer driver for your dot matrix printer you should select the highest dot resolution that the printer is capable of. If the driver has a Dithering option, you should also select "Line Art" or the finest dithering resolution that is supported. Some dot matrix drivers also allow you to set the intensity or darkness of the printing. If your printer supports this feature, you should set the intensity to the darkest level supported.