Create ruled boxes with the box drawing tool and use your layout software to apply the desired frame thickness in order to make precise corners on your boxes. Do not use individual rules to create boxes, as it is very difficult to get the corners to meet exactly.
If you want your frames or rules to measure a hairline in width, specify the thickness as .25 points. Do not use the predefined “hairline” measurement found in the options of some layout applications. This predefined hairline is the thinnest possible line that the RIP can produce. Therefore, while the rule may look fine on a laser printer proof, it will be nearly invisible when imaged at high resolution.