No.9438
The letters and numbers on pencils determine its hardness and softness, hard pencils are graded with an H, and go from H1 (least hard) to H12 I think? (Hardest), these pencils have smaller lead cores and will trace gray lines, perfect for architecture and designs
Pencils graded with a B are soft and have a bigger lead core, they go from B1 to B12 exactly the same like with the H line, and are used more in arts, they work better for shading. HB is the middle ground from both worlds, often referred as number 2 (idk why)
I suppose for your needs it's better to go with a pencil of the H line, preferably one with a number not that high, as those will leave a very faint trace