Abstract: A fixing device, for fixing a linearly displaceable machine part relative to a fixedly supported machine part, has a guiding block (11), a bar member passing through the guiding block (11) in a bar guiding mechanism (14). The guiding block (11) has a controllable setting device and clamping members (21) which are provided with through-holes (24) for the bar member. The clamping members (21) in the guiding block (11) are settable by the setting device, between a first position in which the members (21) clamp the bar member and a second position in which the members (21) release the bar member. The clamping members (21) constitute a plurality of congruent plate elements (21) with parallel surfaces. In the release position, the plate elements (21) are located so as to be approximately normal relative to the central axis A1 of the bar guiding mechanism (14) and, in the clamping position, assume corresponding angular positions relative to the central axis A1 of the bar guiding mechanism (14).