Miter Joint
Affiliate link — we may earn a commissionA miter joint is formed when two pieces are cut at equal angles (usually 45 degrees each) and joined to make a corner, typically 90 degrees. Picture frames, door casings, baseboard corners, and crown molding all use miter joints. The mating surfaces are end-grain to end-grain, which glues poorly compared to long-grain joints. That's why mitered trim gets glued and pinned with a brad nailer. Mitered furniture joints often get reinforced with splines, biscuits, or dowels. The joint looks clean because no end grain is visible from the outside.
Why It Matters
Miter joints hide end grain at corners, which is why they're the default for visible trim work. The catch is accuracy. If either cut is off by half a degree, the gap shows. A miter saw with good detent stops and a sharp blade is the minimum requirement for consistent miter joints. Test-fit before you nail.