Quite a few models can fit up to 9, but we recommend only keeping 3-4 to avoid jamming the mechanism of the pencil. We all want to be ready but it's better to be safe than sorry.
Uh huh. Despite the name and the seemingly complex build, most mechanical pencils are quite easy to disassemble. Take your pencil apart, typically starting by twisting off the end cap, then examine the jammed area. The offending piece of lead can be removed as easily as blowing in air or giving the part a light shake.
Despite seemingly making it easy for ourselves, we truly think that 0.5mm is the best size for most people. The thickness is a nice balance in terms of stroke size and durability. 0.3mm is too thin making it easier to snap. 0.7mm is basically indistinguishable from 0.5mm unless you set them side by side, and anything after that point is blasphemy.