come in 4 main colors that correlate with their hardness:
Blue-Grey = soft, Brown = medium,
Brown = x-hard carbide only.
Also the grit plays a role, with higher grits providing
a smoother finish while lower grits provide faster steel
removal and longer stone life.
Knife Atantic Resin Bond
have become very popular lately providing a great mix
of longevity and performance.
Vitrified Bond are in general a little softer and more
forgiving for guys just learning to joint.
provide a mix of popular sizes including some extra wide
and tall ones.