Ok, here is the question. at one company i worked at the extension lines were a thin lineweight about half the size of the actual dimension line. if the dimension line and text were a 0.12 lineweight the extension lines were a 0.4 lineweight. At my current company the extension lines and the dimension line are the same weight (0.12). The advantage to the thin line weight is an extension line is not confused with an object line. I guess i'm asking which do you prefer. myself i prefer the thinner lineweight for an extension line.