Set Family Parameters tool is used to set values for chosen parameters for all elements of a selected family. After clicking Set Family Parameters an element of the family that is to be edited must be selected in the model, which brings up the Set Family Parameters window:
Click Add Parameter to add a new parameter to the list. The Parameter name can be chosen from a drop-down in the box for the Parameter name or it can be typed in the box. Then, a value can be entered for that parameter. Once all wanted parameters and values for them are entered, clicking OK will start the process of setting those values in all elements of the chosen family.