XF (Extremely Fine) - a stamp that has all margins clear of the design with all sides of nearly equal width. Although the term is used to describe centering, particularly on U.S. stamps, it also implies that the stamp is sound in every respect. "XF" should not be used for stamps that have minor faults such as light creases, small thins, tiny tears, or faded or dull color and should never be used for stamps with larger faults. The early classics are given slightly more leeway in the description of XF, since well centered stamps are the exception, and the margins need not be huge, but in all cases the margins should be nearly equal in size. Although the stamp at right is nearly XF in centering, the left margin is slightly smaller than the right. Well centered stamps of this particular issue are not rare enough to elevate this stamp to XF status. The example is sound in all respects, no tears, thins or creases, the color is fresh and the cancel is sufficiently light to elevate it to XF status if only the centering were better.

XLH (Extremely Lightly Hinged) - "XLH" is something of an oxymoron, akin to being partially pregnant. For those who collect "never hinged" any sign of hinging is a kiss of death. Still the term exists; we have even seen variations like XXXLH, and it is unlikely to come into disuse.