Saddles (carriages) sliding over guideways, are provided with parallel or tapered gibs which can be adjusted by screws, to allow for a sliding motion without affecting the precision of the travel. Straight gibs are packings, adjusted by the setting screws square with the guideway. Figure 5.35a gives the dimensions of straight gibs used for flatways. The gibs are locked in a set position, by locking the set screw with the help of a check nut.