Radius gauge set (bend diamater ruler), metric

A set of rulers for measuring different radii. Each ruler includes a small hole for threading them together into a single bundle.
Here with diameters 4, 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, 22, 24 and 25 mm.

The convex shapes (outer radii) form a 180° arc (creating half-circle profiles).
The concave shapes (inner radii) form 90° arcs (quarter circles), with tangential legs extending beyond the arc to create a right angle.

"Main" refers to the rulers with letters engraved (depth of 0.4 mm).
"Letters" refers to the inlays intended to optionally fill the engravings with a contrasting color as seen in the photo.

(Note: the photo shows older / longer versions of diameters 15, 20 and 25 mm. Their lengths have been reduced afterwards)