For all INCRA Precision Rules & layouts. As you see in the photo, the micro-fine guide holes on INCRA rules are designed for a perfect mark with the 0.5mm lead size in your mechanical pencil. This design elevates the inexpensive .5mm pencil into a precision marking and layout instrument.
All of the marking holes in INCRA rules require a 0.5mm lead size. Some pencils on the market have .7mm lead, but these will not work in Incra's precision marking holes. The eraser removes any errant marks quickly without residue or abrasion.