Gehmann 522B-35 Fullbore Front Iris 4.0-6.0 The 522 series front irises are designed for the Gehman 529 Series and the Rightsight front sight assemblies.These large 30MM irises offer an improved field of view, allowing shooters to often see the number boards in addition to their target. The 522 series comes without cross bars, giving the shooter the "floating aperture" appearance. Aperture Range: 4.0mm to 6.0mm Thread: 1-1/4"x28