So much for their claim to have 50% bigger butts then!
Found one ancient old packet for the 1x, 15ft, 7lb leeda - butt is 0.018" or 0.4572 millimetres. Or it was, on that old style one!
Have had a copy of Fly Fishing & FT sitting open at a page showing the superglue and needling the leader inside the flee line. Very neat. will give it a go one day (but not one for doing on the riverbank).
So, undoubtedly I'll now go away and experiment with leaders of varying butt diameter for a while. By experimenting, I mean go away and buy loads of different brands, try them in inconclusive, unscientific tests, chopping 5 feet off of the end of my favourite Smallstream in the process, before finally reverting back to using the Leeda ones anyway...
i,