Mortise-and-tenon joints are a traditional Chinese technique for joining wooden structures, used in buildings, bridges, furniture, and window frames.
A tenon is a small projection on one piece of wood that fits into a corresponding mortise—a recess, not a hole—in another piece, locking the two securely together.
Known in Chinese as "sunmao," mortise-and-tenon joints were the standard joining technique across China until the late 19th century, when mass-produced nails became widely available.

Source：Changsha Evening News