Metal bar supports usually are made of plain or stainless steel wire and are one of the most common types used. Lower portions of wire supports may have a plastic coating to prevent rusting, or are manufactured in whole or part of stainless steel. Both types can be used where light grinding or sandblasting of the concrete will be done. Precast concrete bar supports usually come with two wires cast into the support's center. The wires are used to hold the support against vertical forms or to hold the concrete bar in place by tying it to the reinforcing bars. Concrete bar supports are also available plain (used to support bars off the ground) or dowelled (cast with a 2.25-inch-deep hole in the center so that a #4 rebar can be inserted into it). Cementitious fiber-reinforced bar supports are available in two types: plain and with wire. Most are chemically inert and bond naturally to the concrete. Both types can be used for both horizontal and vertical reinforcing steel support. Many all-plastic bar supports can be used for both horizontal and vertical reinforcing steel due to their snap-on action or other method of attachment. All-plastic supports offer the advantages of being lightweight, non-porous, and chemically inert to concrete.