La Pavoni Lever Sight Glass Brass Washer code 313004 used inside the sight glass retainers, both upper and lower one.
The washer compresses the silicone seals inside the retainers, in order to seal between the glass tube and the two gaskets.
La Pavoni Lever Sight Glass Brass Washer code 313004 is no 100 on the diagram.
Size: 14.5×9.5×1.5mm