What do the sizes of the sawblades signify? How do I know what size blade I need?
Saw blades are sized by the teeth per inch, the more teeth per inch, the finer the blade. Furthermore, standard saw blades are codified in a simple numbering system, the lower the number, the finer the blade and the more teeth per inch. For example, a #5 is finer than a #7.
The numbering for jeweler's saw blades is based off of the standard code; however, they are so fine compared to other types of saw blades, the numbering continues by counting the number of zeros. The finer the blade, the more zeros. The sizes from fine to coarse are as follows : 8/0, 7/0, 6/0, 5/0, 4/0, 3/0, 2/0, 0, 1, 2, 3, 4, 5, 6, 7, and 8. The fraction blade sizes, such as 3/0 are spoken "three oh," three zero," or "three ought."
Because the jewelers saw blades are so fine, they tend to break rather easily. While correct sawing form is very important, choosing the appropriate size blade for the job will help reduce the number of broken blades. Ideally, you should choose a blade that has 2 1/2 teeth per the thickness of the metal you plan to cut. Since it is very difficult to measure the teeth against the edge of sheet metal or wire, many charts are made to help, like the one below. Keep in mind the chart lists the largest blade for the gauge of metal, if you are sawing an intricate design you may want to use a finer blade.