In reply to Removed User: From the Rockfax website:
British Trad Grade - The grade is divided into two parts:
The adjectival grade (Diff, VDiff, ...to E10). This gives an overall picture of the route including how well protected it is, how sustained and an indication of the level of difficulty of the whole route.
The technical grade - (4a, 4b, 4c,....to 7b). This refers to the difficulty of the hardest single move, or short section, on a route.
The British Trad Grade appears to be a mystery to those used to other systems and is thought to be the most versatile system by those who use it regularly. In practice it is now only used for traditionally protected routes (routes where you hand-place your own gear or where there is only very limited fixed protection - bolts, pegs, threads).
How to recognise a dangerous route from the British Trad Grade - Any route with a high E grade and a technical grade lower than the one indicated at the top of the bar in the table above is likely to be badly protected. (eg. E1 4c, E2 5a, ... E6 6a, E7 6b). This is only a general indication though since routes can also be bold within the parmeters indicated above.
Do you know something I don't? I'm more than willing to admit that could easily be the case, but surely higher adjectival numbers mean a less protectable or more serious, and therefore dangerous route. If not than why do they exist?