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've been using McMaster-Carr's part number 116 S70, silcone o-rings, as dampers, for the past 12 years. No need to add anything(grease, etc). They handle the heat of the tubes, without any ill effect, at all. I've had the same rings, on and off, numerous times. Matter of fact; I've still got a number left in the original bag. E-mail me, and I'll send you a few.

UPDATE on the McMaster-Carr part number. It's now AS568A-116. Like I said: I got mine 12 years ago. What I posted was the number off the bag they came in, then. (http://www.mcmaster.com)

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?