The parts in the first pic are parallels, used mainly for supporting stock in a vise but
can be used for much more.
In the 2nd pic with the 2-4-6 blocks (look more like 1-2-3)are 5C (most likely) collet fixtures
Used for holding round or hex or square stock depending on the collet, also in a vise most times.
Allows you to easily flip the fixture in the vise and miill up to 4 or 6 sides.
The blocks are used for setting up or supporting stock too.
Very useful tooling that can be used in multiple ways.