o-ring size for 12AX7 & AT7 dampers?

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)

Hello Magfan: No- never tried silicone on output tubes. I've been using McMaster-Carr's Viton O-rings(size 135) on my output tubes(EL-34, now 6550), for as long as I have the silicones, on the 9 pin miniatures. I've had the same 16 O-rings(two per 6550), on three octets now. Never had a bit of residue, or hardening of the rings, with Viton. The silicon rings I have, are the red ones. Never had any signs of anything leaching out of them either.

The max temp ratings I'd seen(way back when), for Viton and silicone O-rings, were 392 and 400 degrees Farenheit, respectively. Not far enough apart to make much diff, I thought. I've still got a package of the Vitons, from the original order, that I've never had to use, 'cause the ones in service stayed supple, and elastic. I've never actually used an IR thermometer, to see what kind of temp output tubes generate. I'll have to find now(all this has me curious).