In this fourth paper of a series, values of M i are obtained for the late F–K eclipsing binaries HS Aqr, V1430 Aql, HP Aur, and CV Boo. The values of M i lie in the range 1.07 to 0.71 solar masses, both extremes being for HS Aqr. Lacking useful photometry, the equivalent widths of the Na D lines are employed to obtain, for each binary, a relation between the light ratio of the components in the V band and the two spectral types, a method completely independent of integral photometry. The mass of the secondary of HS Aqr appears anomalously small (0.7 M⊙ for its type, roughly G5, obtained from the strengths of the Na D lines). It appears unlikely that definitive photometry will be obtained for these stars, partly because of intrinsic variability. Under the circumstances, it is proposed to test the relationship between rotational velocities and widths of the stellar cross-correlation functions (used for the velocities), the test being based on results from synthetic binaries with known rotational velocities and binaries with known periods and radii. If the tests prove successful, stellar radii can be evaluated completely independently of photometry. Although extensive tests are required, no new principles are involved.