A fluid-operated vise includes an elongate base structure having a generally rectangular top surface. An elongate undercut groove is formed in the base structure and opens through the top surface. A pair of jaw structures are supported on the top surface and are movably positionable therealong. One of the jaw structures includes a fluid-operated movable component for gripping workpieces between it and the other jaw structure. Downwardly facing elongate grooves are formed in bottom portions of the jaw structures and communicate along their lengths with the undercut groove. Elongate key members are positioned in the communicating grooves to maintain proper alignment of the base and jaw structures. The key members also form parts of clamping systems which are operable to releasably retain the jaw structures in place at selected positions along the length of the top surface. Groove and projection formations are provided on side and end portions of the base structure to permit interlocked, end-to-end and/or side-by-side positioning of a plurality of the fluid-operated vises.
