Reinforcing bar sometimes known as Rebar or Re Bar are high tensile steel bars used to strengthen and reinforce concrete slabs and structures. Although concrete is strong in compression it is relatively weak when under tension. When Rebar is set within concrete it greatly enhances the tensile strength. The rate of expansion due to heat of both concrete and rebar are very similar, and this minimises internal stresses and helps prevent cracking. The outside face of the rebar is ribbed to give it a better adhesion to the concrete, the size quoted is the diameter of the core and the actual overall diameter including the ribs can sometimes be considerably more.