Abstract: The device for releasably securing stationarily a finely angularly adjusted shaft in an instrument with respect to the body thereof includes a cylindrical flange formed in the body and rotatably supporting the shaft therein and provided with a plurality of cut-out portions arranged circumferentially spaced from each other, a rotatable clamping ring rotatably fitted around the flange and having in its periphery wedge-shaped recesses the arrangement of which corresponds to that of the cut-out portions, and clamping members each received in the respective cut-out portion and wedge-shaped recess aligned therewith so that each clamping member is interposed between the outer surface of the shaft and the respective recess, thereby permitting the shaft to be releasably secured stationarily with respect to the body by rotating the clamping ring in one direction in which each clamping member is urged against the shaft by the wedge-shaped recess, while the shaft is released to freely rotate when the clamping ring is rot