Technical pens of olde set the various mm sizes that still seem to find favor today. The most popular sizes were, and [at least my] use of them on a 1/8" or 1/4" plan drawing:
0000 = 0.18 mm door swing, window glass, grid lines,
000 = 0.25mm the door leaf, casings, millwork, dashed overhead,
00 = 0.30 mm most of the heavy lifting, walls etc
1 = 0.50 mm outlines to emphasize edge of slab, outline of elevation,etc
Know that these assignments are personal - most offices will differ somewhat. Go to
www.OnLand.info for some nice office standards type discussions. [Edited to correct web address...]
With computer printers the 0.13 lineweight is very usefull and should be used as the thinest line, in lieu of 0.18. I find the 0.10 line gets lost when contractors use field office copiers to get a second generation copy.
Personally I thought the pen range was skewed to the middle, 0.25 and 0.30 are too close for me. I now have remapped my pens to have a equal percent of increase (roughly 30%) from pen to pen, while retaining many of the old familiar mm sizes I "grew up with":
0.13
0.18
0.25
0.35
0.50 Archicad pen 1, typically the wall outer skin.
0.70 Here and heavier are special use - presentations, borders, grade cut, etc.
1.00
1.40
Generally speaking your drawings are easier to read and to manage over time if your restrain yourself to 4, maybe 5 pens for semi-universal use.
HTH
Snap
