The dimensions of rivets and of the plates at the joint may be calculated by the same rules as for single bolts. If it is a joint subject to tension, as in Fig. 143 the effective strength of the joint and of the plate is the resistance of the cross-sections a b and c d to tension, and of the cross-sections b e and c f to shearing. If it is a joint subject to compression, as in Fig. 144, the effective strength is the resistance of the section g i h to compression. Hence, in a tensile lap joint the size of the rivets should be as small as possible, and the sections of the parts a b c d as large as possible; and in a compressile lap joint the size of the rivets should be as large as possible.

Lap joint is the name given to a riveted joint when the plates overlap each other. In a single rivet lap joint, as in Fig. 145, the whole tensile or compressile strain being divided amongst the spaces between the rivets determines the interval of them. And the whole shearing strain being divided amongst the sections a b, c d, etc, determines the amount of overlap. Fairbairn considers that the strength of such a joint under tension is only 0.56 of that of the solid plate of the same general cross-sections.

In a double rivet lap joint the amount of overlap and the intervals between the rows of rivets both ways, and the size of the rivets, are all determined by the above considerations, and by the rules for bolts. Fig. 146 shows the joint recommended by Humber for tensile strains.

Fig. 147 shows the joint he recommends for compressive strains.

In practice the diameter of the rivets is generally made a little more than the thickness of the plate, and the interval is from 2 to 4 times the diameter, according to the closeness of the joint required.

The practice in H.M. Dockyard at Chatham, in the construction of iron ships, is to use rivets rather larger in diameter than the thickness of the plate, and at intervals from 2 to 4 times the diameter. Thornton states that a watertight joint can be formed with single riveting at intervals of 4 diameters; double riveting is commonly used, the first row being placed at a distance of at least one diameter (of rivet) from the edge of the plate, and the second row at about 3 diameters from the first. These rules determine the length of what is called the butt-plate, or fishing-piece. The rivets in the second row are placed directly opposite those in the first row, and not diagonally opposite the spaces. In all exterior plates the outer rivet-holes are countersunk and the rivets hammered flush.