Michael 182 wrote:

Hate to be dense (not that I have a choice) but does the "double-thickness
cylinder in the center" mean something like a grommet?

Something like one side of a grommet. When used in conjunction with the mating
flat washer, the two washers essentially form a grommet. IIRC, I bought the washers
for the jacks in my aircraft at a local electronics store, but I may have had to
order them.

George Patterson
Love, n.: A form of temporary insanity afflicting the young. It is curable
either by marriage or by removal of the afflicted from the circumstances
under which he incurred the condition. It is sometimes fatal, but more
often to the physician than to the patient.