Many pencils across the world, are graded on the European system using a continuum from H (for hardness) to B (for blackness), as well as F, a letter arbitrarily chosen to indicate midway between HB and H.
It is a myth that F stands for ﬁne; F pencils are no more ﬁne or easily sharpened than any other grade. The standard writing pencil is graded HB. This system has been developed in the early 20th century by Brookman, an English pencil maker. It used B for black and H for hard; a pencil’s grade was described by a sequence or successive Hs or Bs such as BB and BBB for successively softer leads, and HH and HHH for successively harder ones.
The various graphite pencil grades are achieved by altering the proportion of graphite to clay: the more clay the harder the pencil. Two pencils of the same grade but different manufacturers will not necessarily make a mark of identical tone nor have the same hardness.