It doesn't really mean much in the big picture and probably no reflection on the manifold that Ken highlighted, but I took a look at that guy's other listings and saw the Buick aluminum drums. He does the classic, and to me ultra annoying, thing in the description. He lists them as "about 12" diameter". This is a guy who doesn't know crap from shoe polish about brake drums. Almost as bad as the frequently seen "looks like plenty of meat". Arghhhhhhh! You only get about .060 of wear/turning on a drum before it's too thin for safe use (especially on a composite like these). Use a drum mic, not a tape measure or "calibrated" eyeball. Back to our regularly scheduled programming................