Here are the general lengths specified by the different numbered length guards:
Grade 1 - one-eighth of an inch (3mm)
Grade 2 - one-quarter of an inch (6mm)
Grade 3 - three-eighths of an inch (9mm)
Grade 4 - one-half of an inch (12mm)
Short haircuts are generally appropriate for most men, but are especially well suited to men who lead active lifestyles, athletes, those who work outside, or those who want a style with minimal maintenance.