Automatic, or mechanical, pencils are either plastic or a blend of plastic and metal and they hold several leads that refill without having to re-load each time. Of course, there’s never any need to sharpen the smaller sized leads as you do with standard pencils. Another advantage is you’ll always have a consistent line. For drawing, I prefer pencils that hold 0.3mm, 0.5mm, and 0.7mm leads. Larger leads are simply too bulky for fine lines, but are nice for covering larger areas. My biggest pencil is a Staedtler Mars 780, which holds 2.mm leads. These require a specialty sharpener. This is a well-rounded grouping, but other sizes are available, too.
Leads for pencils are not graphite, which would make them too brittle; most are carbon, polymer, or ceramic. Of course, you’ll select sizes to match the pencil. But, here it gets a little tricky because there is such a wide range of soft-to-hardness options.
The standard range from hardest to softest is: 4H, 2H, H, F, HB, B, 4B, 6B.
An HB is a good middle choice, but you’ll want also have soft and hard leads on hand, too. These come in bulk containers, so once you decide, you’re committed. The choice also depends on how hard or lightly you press on the paper. Everyone is different and a heavy hand will break softer leads. Softer leads also produce a fair amount of dust.
One last tip. Erasers included in the tip of the pencil really aren’t the most convenient. Go ahead and invest in an inexpensive holder with eraser refills.