Drafting
Drafting Pencil, drawing with a template
Drafting (sometimes Draughting in British English) is another name for technical drawing. There are a number of requirements specific to this style, which may not be needed for other types of drawing or for writing...
Thin sleeve and narrow barrel: important for two reasons...
Gives a clear view of what you're drawing, with less pencil near the tip to block your view.
Lets the lead get very close to a ruler or template. A thick conical surround would keep the lead away from the edge, and tend to make it jump upwards as you push it against the edge.
Range of ISO standard widths available. For writing and general drawing, 0.5mm and 0.7mm are popular, but technical drawing usually requires adding at least 0.9mm (or 1.0mm) and 0.3mm (or 0.35mm). The ISO standards cover both wider and narrower widths than these, but they are not commonly available in pencils.
Other things that may be important for drafting...
Fixed sleeve: sliding sleeves allow more lead to show without having to click the button, by being pushed up as the lead shortens. The edge of a rule or template may also push the sleeve up, though, leaving too much lead free, and risking snapping.
Good grip: technical drawing will often involve drawing for a long time, so comfort is important. A good grip will also help to avoid the pencil slipping in your fingers, and spoiling your drawing. A soft squishy grip can be good for writing, but wouldn't give the control needed for drafting.
Retractable tip: If you need to carry the pencils in a pocket (all ISO sizes in the shirt pocket for full geek-cred), a retractable tip may be important. However...
Non-retractable tip: A retractable tip will usually introduce a tiny amount of 'play' in the mechanism. Not enough to be noticeable to most people, especially with a good quality mechanism, but some people prefer completely rigid fixed mechanisms.
Build quality: If you don't want to be replacing a pencil regularly, and it's going to be subject to very heavy usage, it makes sense to go for something that's built to last. Most drafting-style pencils will take quite a bit of use, though.
The range of drafting pencils available has fallen in recent times - most drafting is done using computers these days, so less demand means less choices - some great pencils have been discontinued in the last few years, including favourites like the Rotring 600, but there are still some left