Some of you who have been having trouble with microphonic tubes have asked us for a larger ring like this so here it is. I measured 35mm inside diameter, 44.97mm outside diameter. Slips right onto the glass bulb of your 'antique' triode or pentode preamp tubes. The manufacturer also specs this ring for use on 5U4G, 6L6G and other large 'Coke bottle' tubes. I personally don't see any benefit to using rings on rectifier or power tubes but I'll leave that to you.