This invention is a novel sink rim that is readily adaptable to mounting by conventional drop in, under mount and flush mount methods. By incorporating a thicker and wider outwardly extending peripheral mounting flange (102), a tri-mountable sink rim is created. Having a flat surface on both the upper (197) and lower (199) surfaces of the outwardly extending peripheral mounting flange, the rim may be mounted as a drop in or an under mount sink assembly. By welding the separate pieces to form the sink assembly, substantially square exterior edges (of from about 85 to about 95 degrees, preferably from about 89 to about 91 degrees) are formed. These square exterior edges, as opposed to rolled or beveled edges, create a truly flush mountable rim, overcoming the limitations of prior art sinks. The additional thickness and width of the outwardly extending peripheral mounting flange provide adequate support for the sink assembly when flush mounted.