Leica Genuine Series 5.5 Lens Filter Adapter Retaining Ring 11251 -Clean-
$29.95 USD
Here is a genuine Leica retaining ring for Series 5.5 lenses. It will work with the Summicron-C 40mm f2 and all similar 5.5 threaded lenses (feel free to ask if you're not sure).
It is in great condition and works perfectly.
