HD 156324 is an SB3 ( B2V/B5V/B5V ) system in the Sco OB4 association . The He-strong primary possesses both a strong magnetic field , and H \alpha emission believed to originate in its Centrifugal Magnetosphere ( CM ) . We analyse a large spectroscopic and high-resolution spectropolarimetric dataset . The radial velocities ( RVs ) indicate that the system is composed of two sub-systems , which we designate A and B . Period analysis of the RVs of the three components yields orbital periods P _ { orb } = 1.5806 ( 1 ) d for the Aa and Ab components , and 6.67 ( 2 ) d for the B component , a PGa star . Period analysis of the longitudinal magnetic field \langle B _ { z } \rangle and H \alpha equivalent widths , which should both be sensitive to the rotational period P _ { rot } of the magnetic Aa component , both yield \sim 1.58 d. Since P _ { orb } = P _ { rot } Aa and Ab must be tidally locked . Consistent with this , the orbit is circularized , and the rotational and orbital inclinations are identical within uncertainty , as are the semi-major axis and the Kepler corotation radius . The star ’ s H \alpha emission morphology differs markedly from both theoretical and observational expectations in that there is only one , rather than two , emission peaks . We propose that this unusual morphology may be a consequence of modification of the gravitocentrifugal potential by the presence of the close stellar companion . We also obtain upper limits on the magnetic dipole strength B _ { d } for the Ab and B components , respectively finding B _ { d } < 2.6 kG and < 0.7 kG .