The links of ordinary iron chains are usually made as short as is consistent with easy play, in order that they may not become bent when wound around drums, sheaves, etc.; and that they may be more easily handled in slinging large blocks of stone, etc.

When so made, their weight per foot run is quite approximately 3½ times that of a single bar of the round iron of which they are composed. Since each link consists of two thicknesses of bar, it might be supposed that a chain would possess about double the strength of a single bar; but the strength of the bar becomes reduced about 3/10, by being formed into links; so that the chain really has but about 7/10 of the strength of two bars. As a thick bar of iron will not sustain as heavy a load in proportion as a thinner one, so of course stout chains are proportionably weaker than slighter ones. In the following table, 20 tons per square inch is assumed as the average breaking strain of a single straight bar of ordinary rolled iron, 1 inch in diameter or 1 inch square; 19 tons, from 1 to 2 inches ; and 18 tons, from 2 to 8 inches. Deducting 3/10 from each of these, we have as the breaking strain of the two bars composing each link, as follows: 14 tons per square inch, up to 1 inch diameter; 13.3 tons, from 1 to 2 inches; and 12.6 tons, from 2 to 8 inches diameter; and upon these assumptions the table is based.*