The study discussed in this report was made to obtain data on the relative merits of different types of metal wing spar construction, and to develop methods to be used in the design of those types which the tests indicated to be the most satisfactory for use in practical design. Although it is intended to cover ultimately the entire range of airplane sizes, the work covered by this report pertains only to spars of a size suitable for use in single bay externally braced observation airplanes. This is the second report on the spar tests covered, the earlier report being published as Air Corps Information Circular, Vol. VI, No. 590 (Serial Report 2665), "Progress Reports on Experimental Metal Spars," by A. S. Niles and E. C. Friel. The present report includes not only the more important results given in the previous report, but also gives the results of tests to determine the quality of the material in the spars tested, computations of unit stresses developed, geometrical properties of the cross sections and similar quantities, studies of the stiffness characteristics of the spars, an investigation of the characteristic types of failure, the development of methods to be used in the design of the two types which gave the most favorable test results and revised recommendations regarding future work in the study of the problem of metal construction.