Most manufacturers can produce special brick shapes for special purposes, offering designers a wealth of aesthetic options with relatively little added cost. Today's brick are manufactured either by molding or extrusion. Molded brick can be somewhat easier to obtain in special shapes, especially if the manufacturer already has the molds for the shapes you need. If custom molds or mold inserts need to be built, both the cost of the units and the lead time needed to produce them will increase. With extruded brick, shapes that can be created by special dies or shaper caps during the extrusion process generally require less hand work, and thus may add less to the cost and production lead time. Arrangements may vary with different manufacturers, but many make distinctions among three types of brick shapes: Production shapes are certain commonly used shapes, such as keyed jack arches or stair treads, that the manufacturer runs and stocks whenever it makes a particular type of brick. Catalog shapes conform to specific profiles and dimensions that are shown in the manufacturer's literature, but are made only when they're special-ordered for a job. Custom shapes are those designed and manufactured for a particular project, based on the designer's specific requirements.