This is an impressive wrench. Though just 5 1/2" long and compact enough to slip into a pocket, it works with nuts and bolts in a broad range of common sizes. You don’t need to know the exact Imperial or metric size; the jaws accommodate any head from 5/16" to 3/4" (8mm to 19mm). The three-position hinge permits quick coarse sizing; the jaws then automatically self-adjust to the exact fit as you grasp the handles.