How To Read Metric Rebar Marks on Steel Reinforcing

In order to identify the basic information about the rebar that is delivered to a jobsite, it is important to know how to read the mill markings that are stamped on every bar. This is especially critical to ensuring that your materials match up with the specifications in the plans.

These mill markings illustrate the “soft metric” system adopted by CRSI member mills in 1997 (see our post about metric and imperial markings):


Grade 420 Mill Markings

Images and bar marking description courtesy of CRSI

The top letter or symbol identifies the producing mill and deformation pattern.

The next marking is the bar size.

The third marking symbol designates the manufacturing material — usually either “S” for carbon-steel (ASTM A615) or “W” for low-alloy steel (ASTM A706).

Finally, there will be a grade marking (4 or 5, for 420 or 520) or by the addition of one line (420) or two lines (520) that must be at least five deformations long.

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