I have ordered an O-ring from McMaster-Carr. I had my mechanical engineer take the measurements, and we settled on this one. It’s made from Buna-N, not silicone, as the silicone rings were speced out a bit harder than we judged the Nikon ring to be. These arrive soon!
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Be careful about size. It’s ok to stretch just a bit, but you absolutely do not want the O-ring to be too large, or the integrity of the lens seal will be compromised. Also, make sure the ring you buy is resistant to the usual silicone/PTFE grease you’re going to use on the ring.
I have ordered an O-ring from McMaster-Carr. I had my mechanical engineer take the measurements, and we settled on this one. It’s made from Buna-N, not silicone, as the silicone rings were speced out a bit harder than we judged the Nikon ring to be. These arrive soon!
https://www.mcmaster.com/2418t155