The HfFe 6 Ge 6 -type ScMn 6 Ge 6 - x Ga x and YMn 6 Ge 6 - x Ga x solid solution (0.3=<x=<1.6) have been studied by magnetization measurements, microprobe analysis and powder neutron diffraction. The ScMn 6 Ge 5 . 6 3 Ga 0 . 3 7 and YMn 6 Ge 5 . 6 6 Ga 0 . 3 4 compounds display skewed helimagnetic structures in the whole 2-300 K studied range. The YMn 6 Ge 5 . 3 5 Ga 0 . 6 5 compound displays a helimagnetic structure above 160 K and a ferromagnetic structure below 40 K. In the intermediate temperature range, both structures coexist. Finally, the ScMn 6 Ge 5 . 3 4 Ga 0 . 6 6 , ScMn 6 Ge 5 . 1 2 Ga 0 . 8 8 and YMn 6 Ge 5 . 0 8 Ga 0 . 9 2 display ferromagnetic structure in the whole 2-300 K range. The results are discussed and compared with those of all the RMn 6 Ge 6 - x Ga x compounds (R=Tb-Tm, Lu; 0=<x=<1.0) studied by neutron diffraction.