unless you mean a step up ring?
No it's a step down ring
The terminology does vary, which is an unfortunate confusion. For example, even though B&H calls the B+W 72→77mm (lens-to-filter) adapter a step-up ring, Ace Photo Digital, and many other vendors, call the exact same item a step-down ring. In this case, B&H is actually mislabeling the product - the manufacturer's website (Schneider Optics, the parent company of B+W) calls it a stepdown ring, with the description, "Allows you to attach a 77mm filter to a lens with a 72mm front thread," and consistent with that, the box that mine came in was labeled "Reduzierung" (German for "reduction"). If an in ordnung German company like Schnieder Optics calls a 72→77mm 'stepdown' then 'step up' is probably the correct terminology for an adapter than allows you to put a 77mm filter on an 82mm filter thread - but as I stated, it's semantics (although it led to some confusion in this case).
It varies from lens to lens I suppose... for instance there are some lenses which i've heard can give vignetting just putting on a regular filter, hence why they sell low profile filters...
I agree that mechanical vignetting is lens specific, and you can't predict just based on the focal length(s). For example, I'd have thought that the EF-S 10-22mm would be at risk at the wide end, since it's got an image circle designed for APS-C cameras (no sweet spot) and it already has almost 1.5 stops of optical vignetting. Accordingly, I got a slim UV filter (B+W XS-Pro mount) for the lens. However, a while back I did some testing
and found that I could stack a standard mount (F-Pro) filter and a slim mount filter onto the lens, and still
not get any mechanical vignetting. That test showed me that I could stack a slim CPL onto an XS-Pro UV filter if I was in a hurry.
I might have to give this type of test another try with some lenses on a FF body (especially lenses like the 16-35mm f/2.8L
II and 35mm f/1.4L