Arbor

An arbor is the shaft a rotating cutting tool mounts onto -- a table saw's arbor holds the blade, a drill press's arbor (via the chuck) holds the bit. Arbor size matters more than it sounds like it should: a blade or accessory with the wrong arbor hole diameter simply won't fit, no matter how good a match it is otherwise. Most US table saws use a 5/8" arbor; always check before buying a blade.