FÜHRUNGSEINRICHTUNG

To prevent elongation of a covering tape or ribbon (25) extending over an elongated opening (34) in an elongated base body (2) over which a movable element (3) can slide, the tape or ribbon is retained at preferably both of its ends, by a reverse motion, or one-way lock (50,52). In the simplest form, this reverse-motion lock (50,52) is formed by a leaf spring (63) extending at an acute angle with respect to the tape or ribbon; the tape or ribbon is backed up by bridge-like counter element (54) bridging over the elongated opening (34). If the tape or ribbon stretches, for example due to friction upon movement of the movable element (3) heating, or aging, and the movable element pushes the tape or ribbon in form of a bulge towards a terminal position, it can slide beneath the leaf spring and extend over an end portion of the base body; upon reverse motion of the movable element, the elongated end cannot, however, slip because of the one-way locking feature, thus retaining the tape or ribbon (25) taut against the opening (34) and effecting a good seal to prevent egress of operating fluid, as well as ingress of contamination, such as dirt, extraneous oil or the like.