On Monday, August 24, 2015 at 7:54:12 AM UTC-7, N_Cook wrote:
A large Behringer mixer returns with intermittant loss of one or both
channels due to being used outdoors and dust/damp getting on...
... the hex "nut" part of F connectors is the
same thread of these metal bushed sockets.

If, as seems likely, the thread is 3/8-24, you might consider off-the-shelf
sources, as well
http://www.ebay.com/itm/Chrome-Acorn-Cap-Nuts-10-Pack-Choose-Your-Size-/251065531947?pt=LH_DefaultDomain_0&var=&hash=item3 a74abfe2b

The common electric lamp threaded tubing is 3/8-24 thread, and I recall seeing such
threaded fittings (couplings, decorative bits, and caps) in a wide variety.