They are M3x5, yes they will work if you are not keeping the HDD. If you want to keep both, you can probably grab some at a hardware store.
EDIT
I was wrong, 3.5" drives use 6-32 and 2.5" drives use M3 screws. So it depends on your particular situation, if your referring to a laptop then the screws will work. If its a desktop with a 3.5" HDD then no, you'll need the M3x5mm screws.