Download debian packages manually

Hello! I use OSMC on my RPi 2, its running on a closed network with no internet connection.
I need to install some packages that i have to download manually and install on the RPi.

For example i need libftdi1, but what architecture should i choose when downloading?

Execute on your target OSMC apt-cache show libftdi1 should tell you exactly which package

Thank you for the fast reply.