Some time ago I wrote to Hygain:

Sir,
Our Ham Radio Club owns 2 Hygain 18-AVT vertical antennas.
We are after 2 sets of black plastic shields which fit between the vertical
alloy tubing and the outer cover of the traps,
Can you supply them to us?

Harry



Hygain wrote back:

Sir,
The only parts available are tubing pieces.
Thanks,
Jim Shurden
Hygain Customer Service

Question is, what can I use as a substitute, I have tried truck wheel
cylinder boots, but the carbon in them upsets the apple cart.

Many thanks
Harry