Manual says to use drill bits as gauge but numbers?

Besides fractions drill bits can be called by numbers. The smaller the number the larger the dia. of the bit. A #1 drill bit is a few thousands larger than a 1/4" bit. There are also letter bits. Both letter and number drills are often call out as drill sizes for a hole that is to tapped. A good hardware store should have number drills, not real sure about letters. You should be able to drill charts on the internet to download.
Mike