Abstract: A self-centering vise for holding a sample in a laboratory instrument includes a pair of elongated rails, end plates attached to opposite ends of the rails disposing them in side-by-side spaced relationship to define a guide channel having a dovetail shape in cross-section between the rails, a central shaft rotatably mounted to the end plates and extending between the end plates and through the channel, and a pair of jaws mounted on the shaft in the channel between the rails and extending above and laterally of the channel so as to overlie and slidably contact the upper slide surfaces of the rails for holding a sample therebetween upon the rails.