Mechanical 'drafting' pencils came about to speed up the process. With the advent of various papers and mylar (mat finished plastic), you could swap out the lead type and hardness (to control smudging and reflectivity for print/copy machines) as needed. The original versions used leads as long as the pencil and they were thick...perhaps 3/32" or 2+mm in diameter, and you'd sharpen them on a pad of sandpaper.
That shifted to pencils like above in .3, .5, .7, and .9 mm dia. sizes. .3 was used for witness lines (lightly applied, barely visible lines to guide your hard lines) though rarely used because they were so fragile, .5 was used for dimension lines (and witness lines lightly applied if not using a .3) and hidden lines/dashes, .7 was used for object lines (bold lines that make up the shape), and .9 for printing/writing.
That said, a good draftsman could do everything with a .7 and/or a .9 simply by adjusting the pressure, sharpening the tip (usually by rubbing on a piece of paper), and turning the tip to adjust width. In any case, mechanical pencils are comparatively expensive to refill the leads. But, in either case, be it a mechanical pencil or a plain old wood encased one, you're still sharpening the tip and adjusting pressure to control the result.
Now...you know everything
K2
That shifted to pencils like above in .3, .5, .7, and .9 mm dia. sizes. .3 was used for witness lines (lightly applied, barely visible lines to guide your hard lines) though rarely used because they were so fragile, .5 was used for dimension lines (and witness lines lightly applied if not using a .3) and hidden lines/dashes, .7 was used for object lines (bold lines that make up the shape), and .9 for printing/writing.
That said, a good draftsman could do everything with a .7 and/or a .9 simply by adjusting the pressure, sharpening the tip (usually by rubbing on a piece of paper), and turning the tip to adjust width. In any case, mechanical pencils are comparatively expensive to refill the leads. But, in either case, be it a mechanical pencil or a plain old wood encased one, you're still sharpening the tip and adjusting pressure to control the result.
Now...you know everything
K2
