I needed an o-ring and the "standard" 117 o-ring in my opinion was a poor fit but I am not an oring expert.
The best ring I tried is a 20mm ID 2.5mm cross section.
The best install procedure is to install the oring in the groove and then insert the pickup with a slight twisting motion. Any other method will pinch the oring.
Thanks to Bradd aka DoubleD for the calculations