MARS HB 0.7MM MICRO CARBON PENCIL LEADS TUBE OF 12

Mechanical pencil leads for use on paper and drawing card, designed to fit 0.7 mechanical pencils. The leads glide smoothly and easily over the page, giving even lines for technical drawing or other precision work, and are slightly flexible for higher break resistance. 

What does HB mean?
Pencils are graded according to the strength of their lead. B pencils are softer and darker, more suitable for sketching, while H pencils are lighter and harder, more suited for precision work and technical drawing. HB, the 'standard' pencil lead, sits firmly in the middle as a good all-purpose, everyday pencil, and the numbers increase the further they get from this point.

Does size matter?
Yes. A 0.7mm lead will not fit inside a 0.5mm mechanical pencil as it is too thick, while a 0.5mm lead will fall out of a 0.7mm mechanical pencil as it is not thick enough.