In this case you should have an "Equipment Prototype" as parent for all your clamps.
From your structure in Object Tree put all clamps under "FIXTURE" into an "EP".
You can open the Kinematics Editor for the EP as well.
On EP selected you can also open the Pose Editor and you can select the poses for each clamp.
So you can simply build the different steps of you fixture.
You need a dummy kinematics inside your EP.
Custom create two links and a joint between.
As long as this is not available the EP is not interpreted as device.
It depends on what you want to do.
Robot with Fupa (known as Supercomponent in Robcad):
Robot vendor provides its robot model with seperate fupa (Leoni, Kuka own dresspack etc.)
The EP is more or less a container and you put all the robot and fupa inside.
If you want to load this robot with fupa, you only need to load the EP from Lib.
When you have fixture with different clamps:
Each clamp is its own resource, if you create poses, you don´t need to create poses for each clamp you create the poses directly on EP level.
These are only two advantages. Just play a bit with it.