The M-108 is a 30 cm. ruler with one edge marked in millimeters and the other edge marked in centimeters.
The W-30 is 12 in. in length with 1/16 in. graduations on inch side and metric on other. Also a centering scale.
The W-20 is the same as the W-30 except 6 in. in length.
All rulers are made of flexible plastic.