Abstract: A material tester of minimal thickness is provided. A thin metal plate has in one surface an annular groove, and within the groove the plate thickness is reduced, to an amount less than the groove depth. A flexible diaphragm extends over the central part of the plate and over the groove, and is clamped to the plate by an annular ring overlying the groove. Passages extend in the plate from an edge to a chamber defined by the diaphragm and the central portion of the plate. A supporting structure including a handle is attached to the plate, and conduits extend between passages in the handle and the passages in the plate.