The best marking tool is a specialized knife. I used one of these for years in the custom furniture business. But old eyes have a difficult time seeing a scratched line. So now I use pencils.
In most cases, a number 3 pencil is just right. You can press down hard without breaking a sharp point. And a sharp thin line is required for accuracy.
Sometimes you want to mark gently so as not to indent the underlying wood. For example, marking a center line on a fret board extension or on the sound-hole side of a new bridge. A number two pencil is ideal for this.
A good eraser is very handy.
Stewmac makes a dandy string spacing rule (#0673). It practically guarantees correct nut slot and pin hole spacing. For this tool you need a very hard and sharp pencil. A number 4 or 5 pencil is just about required when using the string spacing rule because it takes a very durable sharp point to mark through the tiny slots in the rule. Good quality drafting pencils are available at any arts and crafts store.
So what pencil brands make the best marking tools? Well it just so happens my wife is a retired elementary school teacher. Over the years we acquired just about every brand and style of wood pencil ever made. Extensive testing resulted. One brand stands out as the best wood working marking pencil ever made: Dixon Ticonderoga. Their numbers 2 and 3 are best by far. However, only pencils made in USA will do. Unfortunately, several years ago, the pencil manufacturing was moved to other countries. Now I will use any quality product, not caring where it is made. In this case, the made in USA pencils are better than the imported versions. For one thing, the graphite is not nearly as good, especially in the number 3 pencils which break too easily. The only way to purchase these much older pencils is eBay.
Faber Castell makes a nice number two. Don’t know if they make a number 3. Below is an image of two Dixon Ticonderoga made in USA pencils. Barely visible on the #3 pencil is the "USA" imprint to the left of the word "DIXON". The #2 was also stamped, but that was sharpened away. Note the silver labeling on this very old #2. USA made #2 Dixons are also imprinted in green ink.
©2017 D.R. Hanna