Plot of 3-mm mass-loss rate versus spectral sub-type for the WRs within Wd1 (red; open (filled) symbols corresponding to apparent binary (single) stars). Comparable mass-loss rates derived via radio observations of field stars are also presented (symbols in black as before; data from Willis 1991; Leitherer et al. 1997 and Cappa et al. 2004). Values for members of the Galactic Centre cluster are given in blue (Yusef-Zadeh et al. 2017). Error-bars are plotted where given in the source material. 3-mm error-bars for Wd1 stars have not been included for clarity but are estimated to be ±0.2 dex; please see the text in Sect. 4.2.2 for further details. Note in some instances a slight offset parallel to the x-axis from the spectral-type marker has been applied for reasons of clarity.