Router bits come in about as many shapes and sizes as there are edges to be shaped, and here's how to understand the basics.
Router bits come in about as many shapes and sizes as there are edges to be shaped, quite apart from bits for cutting dadoes and rabbets, or for trimming laminate. Still others cut grooves, semicircular channels, mortises for hinges, dovetails, ogees, coves, chamfers, nosing, glue joints, and dozens of other profiles.
Router bits are made from high-grade steel, tungsten carbide, or a combination of both. The carbide bits, like carbide-tipped saws, are more expensive, but stay sharp much longer, especially when cutting materials more abrasive than wood, like plywood and particle board. Some carbide router bits have carbide tips that are brazed onto the steel, others are solid carbide.
Router bits are divided into two basic categories, simple fluted bits and guided bits.
Simple bits have one or two fluted cutting surfaces machined onto their length; the flutes extend to the tip of the bit. The double fluted bits cut more evenly, leaving a smoother finish than do the bits with one flute (which often leave a wavy cut line).
The guided bits have a ball-bearing guide at the tip that acts as a guide. Also called a pilot tip, it functions as a sort of mobile stop to ensure that the router’s cutting edge shapes the wood to a uniform depth.
Shanks are a quarter inch to a half inch in diameter.