If you could only have one bit, one that would still make your router the most versatile tool you own, it would be the jack-of-all-trades straight bit. Used with a fence on your router table, a beefy straight bit can make rabbets and tenons, while a narrow-diameter straight bit cuts spline slots, grooves and inlays like a champ. Paired with the right jig, it’ll turn out perfect box joints. Need dadoes? A straight bit can make ’em fast on a router table or via a handheld router used with a guide. Routing handheld with the appropriate guide or jig, a straight bit can cut hinge, lock and joinery mortises, and can even level a tabletop. With a suitable fence arrangement, a straight bit turns your router table into an edge jointer. And that’s just getting started — as you just read, if you add a bearing to a straight bit, it becomes a whole different kind of cutter.
Because they can do so much, straight bits come in probably the largest range of sizes — both diameter and length — of any standard router bit, meaning that you can more easily size the bit to the job. Straight bits are often sold in sets offering different diameters and lengths. Specialized straight bits are also available, such as slightly undersized bits for creating perfectly snug dadoes to house plywood that often arrives undersized of its nominal thickness.