Reading a number of threads on grayling fishing and using bugging methods/ czech nymphing there is alot of talk about weighting more or less heavily to suit conditions, water depth and where you locate the fly on the leader. But what I would like to understand is what for example is heavy, what is medium and what is light? I suppose this would be in the form of grms/ozs but this is not mentioned.

I regard bead heads as tungsten being heavy, std metal gold head as medium and probably glass and plastic as light.

Anyone any ideas though on leaded fly weight as heavy, medium and light as a general approximation without taking in to account particular water conditions? Personally when wrapping lead wire 1 single wrap to me is medium and 2 wraps i.e. one over the other is heavy then again I suppose it depends on thickness of the lead wire. Oh and then there's the pre-weighted hooks e.g. Partridge you just tie over.

Any thoughts?

Let's put it this way. I have some pre-loaded hooks weighing 2 gms and they are seriously heavy. They are not the sort of thing you would want to bounce off your skull in casting, and they are probably the quickest way to turn a nice 4 piece rod into a not nice 5 piece rod if your casting is a bit off.
I haven't yet found water in the UK fast enough or deep enough to justify their use, though I have in Austria.

A range of the Bidoz bodies should provide as much weight as most people are likely to need, and the good thing is that they are a standard size so you should be able to repeat the fly over and over which cannot be said for lead wire and tungsten bead combinations.