Three 28mm Inside Diameter Rubber Tube Damping Rings For 6SN7GT, 6SL7GT Etc.

Slips right onto the glass bulb of your octal based preamp tubes. If you've been having trouble with microphonic 6SN7GT, 6SL7GT etc. you should give these a spin in your old amp. I measured 37.09 outside diameter, 28mm inside diameter.