Answer:
As a shear key, you can select a cross-section from the list that is already available in the model of RFEM 5 or RSTAB 8. For example, if you want to use a pipe for shear transfer, it must already have been created as a cross-section in the model. You can also define a different cross-section by clicking the "Import Cross-Section from Library" button.
For the shear-type plug, you can define your own material by using the "Info About Material" button (unless you activate the "Use column material also for other connectors" check box in the window 1.1 General Data). Thus, the materials of the column, base plate, and shear key do not need to be identical.
Finally, enter the length of the shear key in the text box.