Now surplus to my needs. A Centra Duplex with brand new 3.8mm and 3.9mm inserts - £90 inc P&P
"The Centra Duplex is a new innovation designed to attach to the front of a rearsight unit and provide a significant improvement of aiming accuracy. This unit allows either a ring (see the Duplex Insert product) or iris (see the Duplex Iris product) to be added into the sight picture, providing feedback to the shooter as to how centrally they are looking through the rearsight. This additional cue will lead to a more consistent head position.
Adjustments are provided to centre the ring in the rearsight aperture.
It is compatible with the Centra 'Spy' rearsight, and in combination with the Lens Hood II product it can be fitted to many other rearsights, including the MEC Free Sight, the Centra 10-50 Rearsight, Feinwerkbau, Hammerli and most Anschutz rearsights.
Please note that this cannot be used in conjuction with the Anschutz 6805 Rearsight."