O ring for Retina IIa eyepiece

[madNbad]

It may be buried in the depths of many post but I'll ask about how to protect my eyeglasses from scratches. It's a late model IIa with the black metal eye piece. When it returns from being CLA'd I'll take it to a hardware store and dig through the bins of rubber O rings. Hopefully, someone will have a suggestion to point me towards the right bin.

 

[Beemermark]

If you have a Harbor Freight nearby they sell a plastic divided box with maybe 100 different sized o-ring for $5 or $6. I bought a box a few years ago and I'm always amazed for what an o-ring can come in handy for.