Feinwerkbau 16mm Front sight metal inserts Fit 18mm FWB Sight Aperture type

You are looking at 16mm Feinwerkbau frontsight metal inserts.

Genuine Feinwerkbau part

Instock Size range from 2.2 mm up to 5.4mm

These are metal inserts

Size is  engraved on each insert

If you try to used them to a different brand like Anschtuz or Gehmann, they may not fit properly. They all use the same basic system, but each have a different measurement (tabs each side).