quoin block

corner block

2. A square, relatively flat wood block, often decoratively carved, placed at upper corners on each side of the wood framing around a door.
References in periodicals archive ?
The quoin block is a square, relatively flat block placed at the interface between the gate and the wall.
The products distributed throughout South Wales include lintels and sills, quoin blocks, balustrade walling, York stone paving and Moai heads.