Abstract: A clamp assembly is provided for self-rimming sinks or basins which mount through an opening in a supporting counter structure, where the sink or basin has a plurality of brackets secured at least intermittently around its periphery at positions that are intermediate the height of the bowl. A clamp structure has a generally L-shaped configuration, with a first horizontal arm and a second vertical leg, and a bolt threadably received in and passed through the horizontal arm. Means are provided at the upper end of the bolt for engaging the under surface of the counter. The lower portion of the leg is offset in a direction away from the arm so as to contact the outer surface of the bowl of the basin or sink at a position below the bracket, whereby the bolt is kept in a substantially vertical orientation, and a force couple may be created between the bowl of the basin or sink and the lower end of the leg of the clamp.