Abstract: An apparatus for positioning and mounting sinks to the underside of solid polymer countertops has a framework assembly consisting of a front rail (14) comprising an aligning channel (16), rail assembly brackets (26) and a centering graph (20); side rails (18) comprising template mounting ledges (22, 24) and turn-button attachment means (60); a rear rail (46) comprising mounting ledges (22, 24) and rail assembly brackets (26). A sink positioning/hold-down template (38) comprising a sink positioning opening (42), a clearance opening for faucet hole routing (40), sink hold-down clamp assemblies (44), and notches (50) for positioning permanent sink clamps, is mounted on ledge (22) by means of turn-buttons (60). A sink opening router template (36) comprising a router guide opening for sink (48), an opening for a faucet router template (52), and a faucet router template (32) with router guide openings for a faucet (58), is attached to framework assembly by means of pawl latches (30).