Folks claim they have used them interchangeably; however, I would not do it. Secondly, not sure the OM603s readily screw into a OM617 head / vice versa. I will have to double check. I have seen this posted over and over on all three of the major MB forums. I have never tried it in a running car. I think once the major world debate on this topic raged, I took a #44 and there was something up with it screwing into a OM617 head but that was a while ago. Plus, OM603 is a six (6) cylinder.

From memory, the OM603s are ... #44 bodied nozzle holders

OM617s are #5/4s or #46s.