Oops, not nylon - sorry, brain barf.
They are *vinyl*.
They come in a ton of sizes, so you just gotta get the right size for a snug fit.
I think the 3/16" ones cover the "small" (3mm?) fittings.
http://www1.mscdirect.com/CGI/NNPDFF...2092&PMCTLG=00
These are used to protect the threads on exposed fasteners.
MSC has them rated to 300F, so they should be able to take the heat.
I also found out that Eagle Hardware & Garden doesn't exist anymore.
Lowe's bought the entire franchise out.
-Ted