The Gehmann 23mm lens holder for Gehmann Irises allows a prescription lens to be fitted eye-side of your rear sight. The 501 is manufactured exclusively for Gehmann's latest model irises that have a detachable front thread and not carrying the 1.5x magnified diopter. For all other manufacturers' irises and earlier Gehmann versions that don't have the ability to remove the front attachment thread, see 501A.

• The detachable steel front thread of your iris is removed with the factory spanner (5005) and the 501's adaptor thread is then screwed into the front of your Gehmann iris.
• The 501, now with your iris mounted, is then screwed into your rear sight after loosening the rail carrier's allen screw.
•  Mount lens  (Knobloch 23mm lenses will fit Or take your lens holder to your Optician to get a custom prescription lens cut) in the lens holder which may be slid off the rail for easier assembly. 
• Reposition the lens holder on the rail as desired and lock it in place.
• Positioning the assembly on your rear sight is easy as the attachment has radial adjustment and is secured with the allen screw.