Shinwa A1 and A2 engineer's radius scales are a convenient gauge for measuring radii and rod diameters.
The rod between 0.5 - 6mm can be placed into the cutout on the rule and slid down until it stops and the measurement to 1/10mm is read from the scale below. For measuring sheet thickness one face of the sheet is laid flat on the scaled side of the taper and slid along to measure its thickness.
The arcs on the edge of the scale correspond to radii in 0.5mm increments. Scale A1 has 0.5mm to 7mm radii, scale A2 has 8mm to 15mm radii.
On the other face is a standard 150mm linear scale with 1/2mm divisions.
Hardened stainless steel with deeply etched graduations.