The cap to mine fell off (disappeared) and TE hasn’t been super responsive. These are hard to find.
Anyone know the exact diameter? I can probably find any number of D-shaft knobs online but not sure of the size. Or if anyone has an extra? Thanks!
Just ask TE.
I got mine for 6€ I think.
Thank you! They finally responded this morning. It was $8 US with shipping.
Hmmm. Perhaps TE read this site more closely than their email ! 
CB