i think it's the entire top piece. you'd have to ask them. i got bored last night and had to search a while before finding ANY site that sold aquarium trim, and they are the only folks i could find. i wish i had an 18" tank i wasnt using, i'd send you the trim myself. too bad it's not around 12", i have 3 55's i'm not using. the thing about using plastic screws, and i know people have done it, is that personally, i'd be worried about them giving-way after having pressure on them for so long. either the screws, or the holes cut through the trim. i think i'm just overly cautious, though. i mean, for cryin out loud, even though i've read threads on inexperienced people successfully drilling their own tanks, for some reason i feel the need to wait for you to do yours before i can do mine. im an idiot. i'll see if i can find some other places that slang aquarium replacement parts in the interim.