Retained by a squared pin. Feedback suggests that these may need modifying in order to accommodate the locating pin of the 101 series cars. However the AR Giulia 101 series Giulia Parts Book does not indicate a changed part number. That is one of the joys of Alfa Romeo ownership.
 
Part Name: Sprint Boot (Trunk) Lid Catch Return Spring
AlfaStop Product Code: 1CWF164
Original Alfa Romeo Part No: 1493.46.007
Model: Guilia 101 Series, Giulietta 750 & 101
Quantity Per Car: 1