Weld
Command - PrB_Attach
This tool allows you to weld one or more parts to a main part.
The welded sub parts will receive a blue or green color by default (if the visibility mode Sub parts is activated).
This allows you to see immediately which parts are welded.
All parts of each welded assembly are merged together into one selection group.
This means that if you select one part then all parts of that assembly will automatically be selected.
This behavior can be disabled (so you can switch between part selection and assembly selection).
To learn more about this see Assembly/Part selection switch
Note: A plate cannot be used as a main part to weld other parts to it. Only profiles can be main parts.
In cases where you really need to weld against a plate (for example the assembly is composed of plates only), then you can convert 1 plate to a strip and use the strip as main part.