I saw it in SQ...was flying from Singapore to Penang, and the guy in front put a medium size trolley bag on the seat, and strap it with safety belt just like it is a human passenger. From the way he carried it I guessed it is a machine tooling (like a block of metal/steel). There is no way u can lift this up into the overhead compartment and also not able to stow under the seat below.
i guess if you strap it down it should be alright in the case