An essential part of any carpentry tool kit are special carpenters pencils. No carpenter worth their salt would be seen dead without a pencil behind his ear!
Different from normal pencils in that they are chunkier and have a much larger lead through the middle, these last longer during carpentry work and don't need to be sharpened as often as a HB pencil for example. Most work-men on site would probably sharpen theirs with a Stanley knife, but you can generally buy a set of a dozen that come complete with a specially shaped pencil sharpener for around a fiver.
They are pretty much essential for marking out rough framing carpentry and roofing work because normal pencils wear out too quickly (especially when working in the wet) and can very easily snap when working with rough sawn timber.
The line is thicker and therefore easier to see when you are using a circular saw, and if you sharpen both ends you won't have to stop what you're doing to sharpen a pencil when the lead snaps mid way through marking the work-piece!
For fine finish carpentry work though, the lead is too thick to mark accurately enough and so I use Staedtler HB pencils, like you used to use in school.
It is really important for accurate setting out that I always keep my pencils really sharp. A thick line could easily be over 2/3mm out if you cut the wrong side of it!
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