In reply to Malpractise:
Given that quite a few hut approaches are graded climbs in their own right - eg the Couvercle (F+), Conscrits (F) and the Ecrins (F) - I'm not sure that suggesting that the Tryfan and Snowdon ridges are *only* hut walks is particularly illuminating.
I think Crib Goch and Bristly Ridge would be F.