Coupled gauges are those made in couples, each couple being fitted accurately together, so that when the two are put into contact the surfaces which adjoin each other shall exactly coincide and touch, the portions which touch having the same shape and dimensions. A couple of this class are shown in contact with each other by Fig. 723, and another couple are shown by Fig. 728. Such gauges are required for planing gaps or grooves in guides, slides, and similar objects; and both the gauges of any couple may be prepared previous to commencing to plane either the groove or the ridge which is to fit therein. Coupled gauges resemble all other sheet gauges in having their names painted on the broad sides, and in being kept for reference as standards, and also as references when an object is to be repaired after being worn, or when a new one is to be made to serve for the old one. Fig. 727 represents the male-guage belonging to the gap-guage, shown in Fig. 728, and in this Figure both are seen coupled together.

Coupled gauges are also denoted by Figs. 729 and 730, in which the angular gaps or mouths of the guages have bottoms with curved corners. Gaps of such shapes are required for planing the junctions and corners of a great variety of objects, such as the junctions of tee-heads with their rods or bars, bottoms of guide-gaps which are curved, outer corners of slides, entrances or mouths of plummer-blocks' gaps, corners of guide-blocks, crank-arms, guide-bars, lids, and baseplates.

Fig. 732 denotes a couple of gauges that are used in a manner similar to that of the gauges shown in Fig. 728, with the difference of the gap not being in the middle of one edge; by this means the ridge and groove to be formed by planing will fit each other, and also be in their proper places after being shaped.