I don’t know about an exact skinfold, but a natural guy who is committed to excellence can usually maintain a great six pack year round.
Just completed a CKD and reduced my BF from 10% to 7%. Lost a measly pound of muscle in six weeks. My ab skinfold is holding steady at 6mm but I wouldn’t say I had a great sixpack unless tensing under good light conditions.
Totally agree with Heb, as I would expect to have a sixpack from the ‘a sixpack is all due to diet’ brigade but I just haven’t got the mass to show off!
I’m back to high carb diet now and still hope to have 6mm on abs or its back to ketosis.
Also I think fat distribution is a very individual thing as I have 11mm on thigh, 10mm tricep. Definitely lost the ab fat primarily, then the arms but thighs didn’t change.