Turn a carpenters folding rule or metal rulers into a marking gauge / depth stop. By tightening the lever the position of the ruler can be fixed.
Printed in place.
Best printed flat - as designed. Supports are required only towards printing bed, but no inner support. After printing the lever might be sticky. To loosen it gently slide e.g. a flat knife between lever and housing.
Design updated to support thin metal rulers. Don't tighten lever too much, otherwise ruler might cut into clamp.
-- [2019-05-12] Support for thin metal rulers (ruler bed raised if ruler thickness < 2mm)
The bridged parts over the ruler can usually be printed without inner support. However, for very broad rulers (>20mm) you might need to experiment with your printer settings. I am using printing temperatures at the lower end for fast cooling. If the bridges sag to much with your printer config you might require inner support.