Do not know the (exact) size but I bought an o-ring kit for watches. From Amazon I think. From: [email protected] <[email protected]> on behalf of Wallace Gasiewicz via <wallydoc=[email protected]> Sent: Friday, May 3, 2024 4:08 PM To: [email protected] <[email protected]> Subject: [HP-Agilent-Keysight-equipment] Attenuator "O" Rings ? Does anyone know what size and where I could get "O" rings for my HP 8714 VNA.Attenuator?? One is not there and attenuator is not working properly. wally KC9INK