There are four Cradle Angles in every Archivist. There are left and right Cradle Angles, as shown in the picture. The purpose of the Cradle Angle is to support the Cradle Wing. The Cradle Angles are adjustable in slots in the Cradle Base to accommodate different thicknesses of books. The hole in the cradle angle is to accept a Bicycle Skewer, which is a cam-style clamp that locks the Angles and Wings in place. Additionally, there is a prototype cam-style angle adjuster for these parts, to make the angle of the cradle adjustable. I will add it to these pages when I have time.
DXF of all Wood Parts: