To permit quick registration against the edge of a workpiece, each of these rules has a hardened steel hook at one end.
A cam-action mounting bolt secures the hook but releases with a half turn, letting you reverse the hook to use any of the four scales. Hook projects 1/4" for the 6" rule, 5/16" for the 12" and 18" rules, and 3/8" for the 24" rule, letting you reach past relieved corners to register against a flat surface.
The 3/64" thick tempered spring-steel rules have black-filled markings on a satin chrome finish, graduated in 8ths, 16ths, 32nds and 64ths. Length by width listed.
Made in USA.