Are you trying to hold 3 parts in one vise?
If that's what you're trying to do it's going to
Be next to impossible to do.
You can hold 2 parts (one on each end of the vise)
but that center part will most assuredly come
flying out of the vise.
If you want to make 3 parts, I would make them
from one long piece then saw them apart and
cut the bottom off.