Straight Bit

A straight bit cuts a flat-bottomed, vertical-walled groove or recess -- no profile, no bearing, just a plain cutting edge running parallel to the bit's shaft. It's the single most-used router bit in most shops, cutting dados, grooves, mortises (especially with a template and guide bushing), and rabbets, and serving as the base bit style a huge share of jigs and templates are designed around.

Straight bits are sized by diameter (matched to the width of groove needed) and by cutting length (how deep a pass it can safely make), and are available in both high-speed steel and carbide-tipped versions -- carbide holding an edge far longer, especially in abrasive sheet goods like plywood and MDF.