Feinwerkbau Clear 20mm inserts for 22mm Sight 2.8mm up to 5.8mm #1780.8xx.x

These are actualy 20mm in diameter and 18mm at the step down
These are used in the what is called 22mm or M22 foresight sold by various manufacturer like Feinwerkbau
Genuine Feinwerkbau part
Size range from 2.8 up to 5.8mm
Size is Laser engraved on each insert