An assembly includes a rotor disk, a rotor blade and a root spacer. The rotor disk includes a slot that extends longitudinally into the rotor disk. The rotor blade includes a blade root arranged within the slot. The root spacer is arranged with the slot between the rotor disk and the blade root. The root spacer extends longitudinally to a spacer end, and includes a grip element and a plurality of notches. The grip element is arranged at the spacer end laterally between the notches. The grip element at least partially defines the notches. The notches extend radially and longitudinally into the root spacer.