The magnetic properties of the HfFe 6 Ge 6 -type ScMn 6 Ge 6 - x Ga x and LuMn 6 Ge 6 - x Ga x compounds (0.25=<x=<1.5) have been investigated in the temperature range 10-600 K. The low Ga content compounds (x=0.25) display linear variation of the magnetiztion in the applied field range 0-1.5 T. The Ga-rich compounds (x=<1.00) display ferromagnetic behaviour with maximum magnetizations of 11.4 and 10.5 μ B /f.u. for the Sc and Lu series, respectively. The magnetizations of intermediate compounds display field induced transitions, and metamagnetic behaviours are observed for x=0.65 and 0.75. The threshold fields decrease with the temperature. All the studied compounds order above the room temperature. The ordering points decrease as a function of the Ga contents from T N =507 K (491 K) for Sc(Lu)Mn 6 Ge 5 . 7 5 Ga 0 . 2 5 to T C =378 K (324 K) for Sc(Lu)Mn 6 Ge 4 . 5 Ga 1 . 5 . The evolutions in the three non-magnetic R series RMn 6 Ge 6 - x Ga x (R=Sc, Y, Lu) are discussed and compared with the evolution in the pure ternary RMn 6 Ge 6 compounds.