Are reinforcing bars used to increase the tensile strength of concrete. Rebar comes in standard lengths of 60' and are cut to desired length and bent as required. All bars must be bent without heating except as permitted by the engineer. #5 rebar means that it has a diameter of 5/8 ", #4 rebar means that it has a 4/8" or 1/2" diameter. #4 is the minimum size that can be used for a single family residence. Rebar should be tied to prevent shifting during the pouring of concrete. Varies from 3/8 " - 2 1/4 ".