Orbital period against eccentricity of the B-type binaries in NGC 6231. The SB1s are shown in red, with the candidates for harbouring compact objects in green, the Fourier disentangled SB2s in blue, and the SB2s identified in Paper I in purple. Open faced symbols indicate systems that have eccentricities that do not pass the Lucy-Sweeney test (e/σ_e ≤ 2.49) and so are consistent with being circular.