To connect two perpendicular boards with screws, they must be set exactly at right angles. Only after that you can drill the pilot holes for the twist screws. Smaller and medium-sized boards can be fixed in a straight line for drilling and screwing, a wooden instrument made of scrap pieces of wood. In this device, the vertically and perpendicular plates are fixed by several wooden wedges and thrust blocks screwed to the base of a piece of plate..