Plastic. Yellow with black print. Used to identify bolt diameter of US bolts from #4 to 1″ and Metric bolts from M3 up to M22. Identifies US nuts from #6 up to 5/8″. Includes a 3-D thread checker, which will identify thread pitch of US bolts from 2.5 to 40 windings and Metric bolts from .70 to 2.5 windings.