Abstract: A shaft locking or brake device for use with a guide shaft or rail of a linear motion system includes a pair of clamping members enclosed within a housing and an actuator. Referring to FIG. 1, the clamping members (26, 28) have specially contoured cut-outs (38, 40) which surround an axially sliding shaft or a rail (22) of a linear motion system. The clamping members (26, 28) carry pivot pins (30, 32) which serve as a fulcrum against the interior surface of the housing (24). A lever arm extends (34, 36) from the lower end of each clamping member (26, 28) and engages two links (52, 58) of a toggle mechanism which are pivotally connected by a circular toggle disk (54). When the shaft locking device is actuated by a handle (58) which extends from the housing, the toggle mechanism pivots the lever arms outward (34, 36), which in turn causes the clamping members (26, 28) to pivot around their respective pivot pins (30, 32) causing the clamping members (26, 28) to move inward and frictionally engage the shaft (22).