Ahh, are you a member of that site ,err detailing world or something its called

good advice there..
They are plastic and appear to be moulded gloss black and to the front edge there is a lightly perforated area to help break the black to glass.
Ill add a picky if it comes out in a minute.
Gaps, theres oithing obsesive about them

just that it only takes a little effort to get them to look right, ok sometimes it takes a few mods but usually unless something is bent then they can be aligned, you just have to understand where its wrong and what sequence of adjustment will correct it, or get it as near as is possible, end of the day , you have to ask does it look about right and if yes then its sorted,
it takes more effort to fit the bliddy big heavy (but nice)westie towbar.
mm