Lambretta tail light lens screw for series 1 and early series 2Two are required to hold the lens in place.
The Complete Spanner's Manual: Lambretta Scooters by Martin 'Sticky' Round Third Edition 8100072
The Complete Spanner's Lambretta Kit Book
Eibar Lambrettas 1954-1989 by Jaime de Prat Salomone
The Unofficial Lambretta Manual Update by Mark Haines