This is the question that seems to come up with anyone who isn t the most advanced of users. There are so many options, so many designs and configurations it s overwhelming to some, especially those who never knew there were any choices.
I m going to try to clarify and simplify the selection process for you here. But first, I want to talk a little about the saw itself, since choosing the wrong saw can create real headaches when it comes to trying to buy replacement and specialty blades. Keep in mind not only the size of the saw, but the size of the arbor when selecting a new power saw. Or picking up an old one at a yard sale, estate sale, etc. There are some great old table saws out there, like the old, solid-as-a-rock Sears models that have 3/4 arbor shafts, for example. Then there was the huge batch of Asian-made 10" miter saws on eBay with 1" arbors. With cheap OEM blades on them. When I saw those, I knew in a few months I d be getting emails from folks looking for new blades for the bargain saws they bought - blades no one makes. I was right. And those bargain shoppers found out it s almost impossible to get blades off the shelf, that if they re lucky, they can get one bored to fit - at a price.
Almost all power saws for the American retail market from about 8" to 10" come standard with a 5/8" arbor so that's what blades are made for. Anything 12" and larger comes with a 1" arbor. DeWalt makes some 12" miter saws that come with a reducer so you can use either arbor size and there are some 12" industrial double miters that (like Pistorius) that have a 5/8" shaft. But other than those, the standard arbor sizes are about written in stone so if you re shopping for a new saw, stick with them.
Okay, now about those blades...
Size (or Diameter)
This one may seem pretty obvious but once in a while I run across someone who wants to use a blade that's a different size than their saw (sometimes to save money, believe it or not). In most cases, I advise against it. First of all, there's the issue of clearance: a bigger blade won't likely clear the blade guard on a miter or radial arm or the throat plate on a table saw. A smaller blade won't give you the depth of cut.
Then there's what's not so plain to see: the design and geometry of the blade. Smaller saws run at higher RPM, the bigger the saw, the lower the RPM. Blades are designed to work in concert with the saw to give you optimal performance. Enough said about that.
Exceptions? Yes, most notably a dado. Most craftsmen will use an 8" dado on a 10" table saw and in fact, that's the only size most manufacturers make - with a 5/8" arbor bore. For the industrial market, a few companies like SystiMatic make a selection with larger sizes and 1" bore, but you'll need a pretty powerful, heavy saw to use it. A 10" SystiMatic dado weighs in at over 10 pounds and cuts a lot of material.
Another exception may be a highly specialized use, by a very knowledgeable professional, such as the one I heard about not long ago where they were using an 8" non-ferrous blade on a 10" or 12" table saw to cut aluminum plate. This was a blade designed for cutting extrusions, not solid aluminum, but these guys understand the geometry and use it to their advantage.