These are actually 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
Typically found on C62, 602, 603, P70, 700, 800, 2602 & 2700

Genuine Feinwerkbau part
Size range from 2.8 up to 5.8mm
Size is Laser engraved on each insert

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If you need a tracking number for your order, please be advised that prices are 
Canada: C$9.00
USA: C$12.00
International: C$19.00

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