Distribution of the 318 Galactic O-type stars in a modified Hunter diagram, using He abundance instead of nitrogen on the y-axis. The fractions of He-rich stars in the slow- and fast-rotating subsamples are indicated, assuming v sin i = 200 km s⁻¹ as the dividing threshold. ON, SB1, and RW stars are indicated with red small circles, blue crosses, and grey circles, respectively.