o-ring size for 12AX7 & AT7 dampers?

How hot do these tubes get? Silicon will only take so much.... Other elastomers can take more heat. EP, for example....
'snug' is good, apparently.
I have DowCorning Silicon StopCock grease, a white/clear grease used to lubricate O-rings.....VERY sparingly. In the industry I worked, the philosophy was to 'put none on and take it all off'....THAT sparingly.

I thought this over.....and low power / pre tubes probably run cooler than output tubes. Don't have numbers in front of me, but silicon is pretty good....
Do you get the 'red' silicon? It has oil in the binder which CAN come out at elevated temps.
The Silicon stopcock grease would be simply to make to ring slick enough that it wouldn't 'roll', but instead would slide down the tube. AND, used in extreme moderation. NO blobs or globs.
I'd be careful and keep an eye on silicon if I tried it on output tubes.

Rod, have you tried ringing higher output / hotter tubes with the silicon? Any problems? Any residue on the tube when you slide the ring off, at least on output tubes?

Tubes must run a bunch cooler than I thought. Even output tubes.
Viton, if memory serves, doesn't take to heat as well as silicon.

I have seen, under EXTREME conditions, NEVER to be found in the home, that an oil will leach out of silicon rings. Not much, but messy.

Their are a few 'exotic' elastomers which take heat better than silion but can be $$$. Doesn't appear that level of nuttiness is needed. Stuff like Kalrez.

http://www.oringswest.com/

More than any rational person would want to know about o-rings.

Post back, or PM me, please.
I have looked at several sites and gotten various answers on temp tolerance of the various elastomers.
I don't even care what they will chemically 'put up with'. Some don't like gasoline or acetone or alcohol or whatever. That doesn't matter, either, to a hifi guy.
Since the silicone and/or Viton seem to be working, I'd skip Nitrile, Kalrez and Ethylene Propolene (EP) since they are simply not necessary.

Be careful to read the envelop temp, NOT the filament temp.