I remember when selling a cue with less than a 13mm shaft you'd get be told it wasn't worth much without a 'full' shaft.
I have a 14mm showcase true hit with an ivory ferule and an original Moori medium on it. it hit's Soooo nice but it feels like a broom handle.
I was experimenting with different size shafts back when I had it made. It turns out I like 12.5 - 12.75 but I can play wit about any size if that's whats available at the time.