When a character has a sheath that is relative to themselves on the larger end of what is anatomically possible. But is still plausible. Do note that a sheath, being effectively a sleeve for a character's own cock and thus the diameter will often match that of the cock, is best measured primarily by its length. But still with some respect to the diameter if it's significantly thicker than what would be expected for its length. Or because the sheath's length is close to that for its type*, and it's also quite thick for its length.
(In this example, feline sheaths.)
thumb #6232156 thumb #6225666 But not if the sheath only has a large diameter, while completely skipping out on any length at all and is effectively just a hole in the crotch with a thick rim. That's a common tagging mistake.
- :Note that different types of sheaths have different sizes that would be considered to be anatomically possible. A feline sheath that's long enough to barely poke out from between the legs (if it were to point forwards) would very likely need the huge sheath tag. But for a canine sheath such a length would sometimes not even be considered to be big.
Related big: