Prismacolor Turquoise Drafting Leads are by far the most popular leads in use today by drafting professionals. Drafting Lead Hardness is something many people have trouble understanding and remembering, but it's fairly simple.
Keep in mind that graphite is the key component of modern lead, however, lead is actually made up of a mixture of graphite and clay. The formulation of this mixture determines its lead grade or lead hardness. The higher the portions of graphite content relative to the clay portion, the softer and darker the lead will be, and vice versa.
There is no real standard of lead hardness or darkness for lead hardness. You may find Lead Grade Scales, or Lead Hardness Guides but most of the time users find what works for them through some trial and error and practice with multiple leads. Regular pencils are called #1 or #2 in the United States, but most Countries use the European "HB" system. H stands for Hardness and B for Black. In the middle there is also an F (for Firm). The more H's in the name, the lighter (and harder) the lead, and the more B's the softer and darker. So HB grade is Hard Black, 6B is extremely soft and dark, 4H is very hard and light. The standard grade for writing leads are HB, which is very close to a Number 2 Pencil which most people recognize. Slightly darker and softer is B, which is about Number 1 Pencil. From the softest darkest through to the hardest lightest lead, the range is usually 6B up to B, then HB, F, and H up to 6H, but some leads go from about 9B through to 10H. As a rough guide, for the USA, #1 = B, #2 = HB, #2.5 = F, #3 = H and #4 = 2H.