Gehmann 522B-35mm Iris foresight threaded 1¼" x 28 Appears as a perspex element

Gehmann #522B-35 Iris foresight

threaded 1 ¼" x 28, appears as a perspex element

Fits art. no. 529 big bore foresight unit “Rightsight” 
Infinitely adjustable iris 

522B-35 adjustment range B: 4.0 – 6.0mm